Hi there Yakisoba,
It seems that many mom's are having the same issues you are. It's a tough one, because often there are roots to these behaviours that have nothing to do with Down syndrome, and other times, may be inflamed because of it.
It sounds like your son needs to exert this additional energy in a different and constructive way. I often ask mom's who have issues with behaviour to look at a post I put together regarding behaviour, where choosing an outlet such as high level activities might help. Your son is the perfect age to begin in the type of activity that I mention in my post of some time ago (Aggression & Behaviour Issues in children with Ds.)
You can read it here: http://www.medhelp.org/posts/Down-Syndrome/A-Suggestion-for-BEHAVIOUR--AGGRESSION-issues/show/1226208
Take a look at the post and see if this is an idea that you might be able to pursue. I have many mom's from my parent group that talk about everything from newborns to adult children with Down syndrome. I often ask my friend who is a PT Therapist for Down syndrome and also an Aunt of a nephew who has Ds, and I have put together something new for my parent group. It is a modified reward chart, that can help instill good, and acceptable behaviours while also curbing the negative ones that we would all like our children to have.
Here is a copy of my information regarding the Reward System:
Behaviours are always certainly hard issues to deal with. A lot of times I have found that kids will continue to do things that they get reactions from, even if the reaction is negative. Simply because it still is attention that they are receiving. Have you tried a reward system? Use stickers on a chart as incentives for good behaviour, and removal of the stickers if he spits or other unwanted behaviours. When he gets 10 stickers in the categories that you put up (like chores or making up bed, putting toys away etc.), then he can get a reward of some sort, whether it is an ice cream, or a day out of his choice etc. But, use this system concurrently for the punishment side as well, so that if he is hitting, spitting or misbehaving, the stickers get removed, and there are also sub consequences like the time outs in addition to the removal of the stickers. I have heard there are great results using this system. I modified it somewhat from a show we have on TV here called "The MOM Show". They use it to encourage good behaviour but I found that removing the stickers is also a great way to minimize unwanted behaviours and it works for my 6 year old step daughter and 9 year old step son. I got the idea when we needed to implement some sort of system for the eldest step daughter who is 11 but has severe learning delays and is also diagnosed with ADHD. I hope that if I need it again for my son (who has Ds) it will work well for him also. He is only 11 months old though, so I am not in need of it yet!
Give it a try and see if you get any results. Short of saying to you, talk to your child and let them know that the behaviour is unwanted and is making you very upset - but I am sure you have probably tried the verbal route. I often suggest martial arts for kids who have more extensive behaviour issues or aggression - but I tend to suggest that when they are around 6 years and older. I have trained children as young as 4 years old, but that is a longer term solution for discipline, health and mental awareness. (If that interests you, see my post in this forum that is titled "Aggression and Behaviour Issues".)
I have other suggestions, but you may want to message me as some of them may be lengthy. My resources are from my 13+ years of policing, being a coordinator of a play group at the YMCA Early Years Centre's, 2nd Degree Black Belt and a university psychology background. Hopefully we can figure something out to help you!
I hope sincerely that one of these two suggestions help, but if they don't I can always find out other information for you.
In addition to anything I have mentioned, please keep in mind, that while I or others may have extensive knowledge in many areas, you should always seek professional medical advice from your own physician, as it pertains to medical conditions or concerns.
Good luck, and if you have any other questions that I can help you with, please feel free to message me directly.
MedHelp Genetics Community Leader;
Children - Special Needs Community Leader;
Down syndrome Community Leader & Ds Group Forum Founder/Moderator