NickyMick, are you the dad or the mom? This seems like a dad thing to talk to the son about.
I happened upon this question by accident when it was recommended as related to my search about something completely different. I clicked on it because I did this when I was 11. After reading the responses here, I felt that I should contribute a different perspective even though it's several years later. This is for someone else who finds this in the future: I think you should strongly consider doing nothing or very little about this.
First of all, let's put this in context. A 12 year old is not "way too young" to be doing this because his body is in the beginning stages of puberty. It would be weird if he had no sexual impulses whatsoever. It's normal for kids to talk to their peers about sex and this can lead to experimentation. It happened with me in fourth grade with two other guys in my class during a sleepover. While I happen to be gay, the other two boys are not and none of us even realized this was a gay thing to do. We talked about girls we liked afterwards—myself included—and not in response to the experimentation that took place. Not a single one of us was concerned about what it meant or even considered the topic of sexuality because we didn't really understand it at the time. Also, it was my two heterosexual friends who wanted to do it and thought of it as a game. I was the one who didn't want to and had to be convinced. I was the only one of us who thought there was something weird about it. Despite that, my hesitance was primarily because I had an unusually large penis for my age and thought I would get made fun of if someone found out. This was in the 90s and I had a very fragmented knowledge of sex and sexuality at 11 years old. I didn't know having a larger penis was considered a benefit and, to this day, I would still argue that it's not. Be happy if you're average. You're simply more compatible with more people, sexually-speaking. Also, my friends didn't know any of this either and I did get made fun of for it.
That was the only negative impact of my dry-humping threesome experience as an 11-year-old: I became more self-conscious about my penis for a couple of years. On the other hand, I learned more about how my body worked and learned why older boys enjoyed masturbation. I'd never had an interest prior to that. My parents had the foresight to teach me about sex when I was a toddler so I was never confused about why it was pleasurable or how babies were made. The more I understood the less I looked for answers. I was the one who had to be peer-pressured into this pseudo-sexual experience with my two male friends—despite being the only gay kid in the bunch (not that I knew at the time)—because I understood what sex was and I wasn't curious. I also understood that sex was something I would become interested in doing with another person later in life and so I just didn't care that much about it.
What I didn't have, however, was context for what it felt like. I knew it was pleasurable but there is a chasm of difference between the pleasure you can experience through common childhood activities and sexual ones. Sexual pleasure also has a very cerebral component that becomes more significant with age. I used to dread the ride to school each morning because bumps in the road would cause enough friction in my pants to get an erection if they happened too frequently in a short amount of time. Physically-speaking, I had a very high sex drive as an adolescent and that persists to a lesser (but still significant) extent decades later. Nevertheless, I never even tried to masturbate at school (this happens more than you would like to believe) and I wasn't eager to engage in sexual activities at all. I was the first person in my class to have actual sex, but this wasn't a result of seeking it out. It was purely circumstantial and I actively wanted to wait until I felt comfortable.
All of that said, I am not every boy that has ever lived. We all have unique differences and would likely react to these situations in our own way. My friends, however, were not adversely affected by the dry humping in any way, either, and we've all grown up to be reasonably well-adjusted people. While other boys might have responded differently to the same situation, overall it's a completely harmless activity under the right circumstances. It's not a bad thing for kids to figure out how their bodies work and if I caught my son dry humping his friend I'm pretty certain this would be my thoughts in order: 1) I wish he used more discretion so I didn't have to witness it, 2) I'm glad clothing is on, 3) I'd tell them I'm not upset, restore their privacy, and let my son know that I trust him to make good decisions for himself or ask me for help when he can't. The anxiety of getting caught is already enough of a deterrent. The fear of disappointing your parents, when they trust you, is also a very powerful thing. Telling kids they shouldn't do something is one of the best ways to guarantee a behavior continues.
As counter-intuitive as it may seem, making an issue out of something like clothes-on dry humping is just not a good idea. It guarantees it will be an issue for your kid if you tell him it is an issue and explain all the reasons why. That's what will stick with him. What comes across in those moments—and I'm sure you can remember a few from your own childhood—is that you did something your parent didn't like. You don't understand why, entirely, when it comes to sex if you're not properly educated in advance. As a result, the reinforced behavior becomes "don't do sexual stuff if I might get caught" and not "I'm too young to be exploring my sexuality" because his body is signaling the opposite.
The best thing you can do to prevent something like this from turning into an actual problem is educating your children about sex in advance in a way that's completely non-judgmental and doesn't leave out any core information. That includes talking about pleasure, where genitals can go, and what orgasms are like as well as their more practical purposes.
I am, admittedly, a weird person but I'm not unusual in regard to how I responded to early education about sex. My experience with early sex education is the common experience. When you grow up without any discomfort around the topic, the worst thing that tends to happen is that you share what you know with others and get yourself into trouble as a result. I was scolded multiple times, by other parents, for correcting their kids about how sex actually worked. I didn't ever even think to talk about anything you'd find outside of a textbook and simply explained the mechanics. Everything I ever said would've been fair game in even the most restrictive sexual education class.
The only things you really ever need to do as a parent is teach your kids how things actually work, trust them to understand, let them know you're always there for them when they need help understanding (or just need help), and remind them that you love them no matter what every single day. If you can do those things you will not have to wonder what to do in situations like this. Trust your kids. Let them know it's okay to screw up and you'll still love them and help them. Create an environment where they trust you and want to talk to you when they're not sure what to do in life. As a parent, you are the #1 biggest influence on their behavior from birth until death regardless of how much you see them in their adult years. Sometimes their behaviors will have negative consequences, but you can always approach every issue—both good and bad—with as much compassion as you are capable. The only issues that stick with your kids are the ones you and others create in response to what they do and yours carry the most weight during their formative years. If you don't want something benign like dry humping to inform negative behaviors in the future, don't make it an issue in the present.
Ask him about it. Tell him he’s only allowed to that in his room and only if the other person is ok with it. Tell him that if they say no or stop then he must listen.
Most boys do experiment with each other, and they usually do not start at that age. I would be extremely concerned as to where they learned how to do it and the mechanics behind it like what taught them to rub against each other. Most boys who do experiment are heterosexual...it’s just a ronde vous if you will. However, considering age, it’s something you should look into. No child male or female should “feel good” someone at that age. If your child does turn out gay or bisexual, accept him with loving and open arms, and please do not turn your back on him and/or kick him out. I’m a Christian, and I will happily accept anyone on the bases that what they are doing does not hurt themselves, a child, any one else, and animals. After all, God said “love thy neighbor as you love yourself” and to “not judge for the extent that you judge the same will be held against you”.
You definitely need to talk to him and ask why he was doing that with his friend and ask how long they’ve been doing it, Tell him it is not okay to do that at such a young age, But it should be you’re desion If u want to give him consequences also ur descion to tel his parents.
When I was about 5 or 6, my grandparents babysat me along with a few other kids from the neighborhood over the summers. I recall dry-humping another boy who was maybe a year younger than m; it was his idea btw. We even took turns. My memory is fuzzy but I think our penises were exposed when doing this. I’m positive, however, that there was absolutely NO penetration, no ejaculation or orgasm, not even an erection, just our penises rubbing against each other’s thighs. We did it because it felt good; can’t think of any other reason. This boy and I never really talked about it as adults. And I didn’t have actual penetrative sex until age 19. For the record, I am a gay man and he is straight (as far as I know). I believe I’m pretty well-adjusted as an adult. I have a good job, no mental health issues, and am sex-positive (meaning I don’t shame or condemn people for their consensual—emphasis on consensual—sexual practices, however unusual it may be.) IMO, things you should discuss with your son, especially at his age, are 1. Whether or not the act is consensual, 2. Safe practices, and 3. How these acts impact him and others emotionally. He’ll be incredibly embarrassed, but not talking about it after being caught could create more tension than acknowledging it. Disclaimer: I am NOT a mental health professional. I can only provide anecdotal advice. OP, you’ve probably resolved things long ago, but I’m telling my story for other parents who may have the same concerns.