I recently read a study where there is pretty conclusive evidence that vaccinations that use Mercury as the preservative are linked to the occurances of autism and possibly ADD.
A previous study that said there was no connection between the two was lead by someone that worked at GlaxoKlineSmith!
So it might be possible that chelation will help if the Mercury has not left their body. There are other ways to force toxins out of the body that are certainly far more "enjoyable" to kids than chelation!
I'll put a synopsis of the study on my site in the next day or so.