As far as I know there aren't any long-term Lithium studies done on children. Prior to my son entering school treating a young child with psych and mood medications is something we would have never remotely considered. My son is 10 y/o with the same diagnoses as your child, w/early onset of Bipolar at 7 and ADHD at 6.
After exhibiting the same behaviors as you described with your child on Respirdol we had to make a heart wrenching decision to hospitalize ours for the first time ever last Dec. Since 1st grade he's had great difficulties functioning in school with his ADHD symptoms and also in most interpersonal situations. However, he was able to cope at home and in family/friends settings. He began having raging mood swings that got increasingly belligerent with everyone at school and home. In addition to this, the Respirdol raised his hormone levels and caused a serious imbalance. Ages 7 to 10 he had been on over 18 different traditionally prescribed ADHD medications. Concerta and stimulants like Folcalin worked for while then eventually stop working or he would have side effects that were either medical or psychological.
When he was hospitalized with great ambivalence we agreed to a Lithium cocktail with Abilify and Imipramine, after about two weeks his mood stabilized.
Its been 3 months now and he's doing exceptionally well, better than he ever has, its like a miracle drug!
Along with structured daily routines, consistant sleep/ADLs schedule and good diet habits; cognitive behavior therapy, positive reinforcements that extends to school and home has unleashed this AMAZING kid!
He's gone from a F student to A-B, he's now athletic (on track team), musical (in marching band, a drummer) artistic (draws Anime art), technology (creates utube tutorials on graphic art and MATH!)
Now that hes able to focus, were seeing skills and talents in him we did not know existed before the Lithium.
But best part of all of this is he's a mostly HAPPY child now... His self esteem and confidence has increased dramatically, right now were just pretty much dealing with "normal tween stuff." Its scary giving him this drug without any real studies or research. So we have frequent labs and heart monitoring done on him and just watch him very closely, so far so good.
Its our hope and goal for him to learn behavioral skills to self monitor and at some point come off of ALL these medications.