There is much co-morbidity (co-existance) of ADHD in bipolar children. The concern, however, is that stimulants sometimes cause an upset to the delicate balance of mood. It is not uncommon to see more anger issues, depression and even psychosis when stimulants are added. It is important therefore to be careful when using stimulant medication with bipolar children. Strattera (atomoxetine) is in the same camp since it exerts antidepressant effects and can cause manic activation in bipolar children.
Safer medications to consider in children with bipolar to address attention issues include tenex, provigil (though I have seen it increase anger on occasion), amantadine, buspar and to some extent wellbutrin (though it can cause manic activation it seems less likely compared to other antidepressants).