Chele, the most common side effects include insomnia, decreased appetite, stomach discomfort, nervousness, dry mouth and sweating. Growth retardation has been reported, but this is mostly counter-acted by taking drug-free holidays. It is definitely uncommon for someone’s head to keep on growing while the rest of his body doesn’t (like suggested in the posting above).
I thing that before a child is put on Ritalin® he should be seen by a child psychiatrist and a child psychologist. Feedback also needs to be acquired from his teachers and even an occupational therapist if necessary. Good luck.