While we aren't doctors, it is a bit awkward, possibly dangerous to actually ask a doc if it's ok to let your kid smoke pot.. There are no physical interactions between marijuana and other drugs, smoking pot isn't going to cause seizures, hear attacks, liver damage etc. But it may have some pharmacological impact (ie. making the stattera less effective.)
If you want an opinion from someone who's been on ADHD drugs; do your kid a favor and throw that shit away, the ADD epidemic is motivated by a combination of drug company profit margins, the educational system's inability to cope with children that don't fit "the mold", and plain lazy parenting. Whatever the reasons may be, thousands of generations of children grew up without the need for mood altering drugs before the inception of ADHD, we've let a handful of people dictate what a normal child is to the entire world.