Adderall is an amphetamine. I would think that she would be the one taking it more so than him.
Although I have seen Adderall (in various forms) used with school age children predominantly, I do know that there are children who wind up on medication before they turn school age. Usually, younger children on it are in a program(s) and need it for focus or behavioral adjustments (not touching others, sitting still, working on projects). It is less common that a 4-5 year old not in a structured program would be given Adderrall as opposed to Ritalin for ADD/ADHD. Most doctors start with Ritalin as it is the granddaddy of these medications. Kids who are dx'd at an early age usually have severe symptoms or a parent who struggles with behaviorally modifying problem behaviors. More and more doctors are trying to manage younger children's behaviors through play/talk therapy and giving parents tools to manage the issues and stressors they have.
If he was medicated for ADD/ADHD, he would have to be seen for follow ups every 6 months or so.