I'd try the Lithium,it is an excellent med for mood disorders, and has been long used with a great track record for several decades.
After one has been titrated to the therapeutic dose for them, bloodwork is then done once every 3 months and then once every 6 months,it's really no big deal,especially when you weigh the good side vs the bad side.
Many kids at first who really are bipolar get misdiagnosed with ADD/ADDHD,docs hand out stimulants that can fuel more manic behaviour.
It also can be possible a child has both disorders,but a reputable pdoc will treat the mood disorder first and then combine meds to treat the ADD/ADDHD.
I am mild Bipolar-II and mild ADD,take a mood stabilizer and was given Concerta (finally)for my ADD, it made quite a difference.
If only back in the early 60's this stuff was more known about,would of saved me a lot of poor grades and spankings.
I'd suggest giving it a try,I find it was better for me than Depakote,which was zombifying,the fatique was bad and with Depakote one has to go for bloodwork too,effects the liver.
Lithium for my family members,after other meds,turned to be the best. One brother has Bipolar-I and untreated he can get violent episodes,sooooooooooo Lithium for 33 yrs has been a huge help to him. I understand everyone is different,but it may be worth trying the Lithium,that your doc would like to go with.
Just my personal feelings.