Some PPs have given you some good ideas! We got a rebounder/mini trampoline 7 years ago and still use it every day (we got one of the more expensive ones and it's really held up). The rebounder and the body sock
http://www.amazon.com/Body-Sensory-7-Sizes-Large-Royal/dp/B005NQV9UQ are go-to items. Any time a kid needed calming down, into the body sock he went. There would be a flair of excitement/activity and then blessed calming. We still use the bean bag chairs we got about 10 years ago
http://www.ahhprods.com/ . The kids would make 'sandwichs' with them - kid in the middle. Finally, one of the things that fed the screen addiction but was healthy was doing Wii Fit and Just Dance. Exercise is your friend and since your guy DC is so small, it's not like cross country is in your toolbox yet. Besides, those games can be done any time of day, any weather. Hugs.
Oh - we also got one of the 'swing chairs' from Ikea and installed it into a joist in the basement. It's near the rebounder. I've got one kid that could swing all day. It's so calming! But, I got another kid that loathed it until he was about 6.