I am not ADD/ADHD but I just want to add general information: sitting still is not a good idea altogether, and prolonged sitting shortens lifespan and leads to obesity. When you grow up and start working, I bet most companies would already have standing desks. I have a standing desk and I use it now, but it is still rare to be offered a standing desk alternative by the employer.

When you have a standing desk, you are free to move your legs and it is actually good to move your legs, shift your weight from one leg to the other and back, or put one of your feet on the footrest for even better body alignment.

There are many bad things about sitting, but one of the worst is that you do not move your body. Sitting still is the worst.

So I hope that when you grow up, this problem will go away for you.