Is he dinking enough water and replenishing? Does he need to see a doctor?
Maybe try sweat block on Amazon. They have wipes as well as deodorant.
I have heard botox injections can help.
He needs to see his pediatrician. Sounds like he has Hyperhidrosis
I got Botox shots! It’s called hyperhydrosis i think, excessive sweating. My insurance covered it!
Try cornstarch and have him shave his pits
Sweat block works for my daughter