ADHD medication is not dosed by age or weight. How an individual dose on a particular dose depends on metabolism, genetics, and neurotransmitter needs. A 300-lb man could need less than your 6-year-old. This primer covers all aspects of ADHD medication:
A Patient’s Primer on the Stimulant Medications Used to Treat ADHD
Penny
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism