It is normal to feel guilty. That is what good, caring people do. It is also very normal to do some sexual exploring at the 10/11 year old age. However, I really don't call what you were doing sexual exploring, as it was more like imitating adult behavior.
And, if this was a one time only event with each child, I tend to doubt if they even remember it...especially at that age.
Telling your mom was a good thing to do because keeping this bottled up inside of you has obviously impacted you. And, her response was correct. So, yes, its time to move on. The only damage done was apparently to your own sense of self worth. And, if you did not have such a good sense of self worth - this would not have bothered you at all. Point being, someone who takes the time to write into a forum, and be concerned about this - obviously has some concerns. However, the reason you have these concerns is because you are a good person!
Oh, keep in mind that your brother is now old enough to want to do a bit of exploring himself. If he starts getting too frisky, that might be the time to say, " hey, I tried that once and it has really bothered me ever since."
Hope this helps. Best wishes.
The truth sets you free, so I'm not going to sugar coat this, but unfortunately, what you did is considered sexual abuse given your age at the time and their age at the time. IF genitals or nipples were touched or any kind of sexual behavior. Don't freak about this either, but it is also considered incest. According to the World Health Organization. That being said, that doesn't mean that you intended it to be that. Obviously not. But that doesn't mean that it won't affect them or you in the long run if it isn't dealt with. I would seek professional opinion on this. The best you could do for them is simply apologize to them. What you want to avoid is them feeling like that is all that they are good for. It may be a difficult conversation to have, but that is where a trained professional can guide you. Also, you will no doubt have to have therapy for yourself. You feel guilt and you have to work through that. The worst thing you can do is carry shame around with you for the rest of your life. It will affect you. You are 16 and you have your whole life ahead of you. Learn compassion and kindness for yourself. May I suggest Ajahn Brahm on YouTube. You didn't know what you were doing and you must be kind to yourself. Don't exile a part of yourself away. You must love all of your parts, including that part that felt sexual. You are human and it is okay.