The dog trainer I go to recons it can be a sign of fustration and offered this as an explaination as to why Dexter has a tendancy to hump any dog in sight when hes on a lead. It does explain alot for him. So now If i know Dexters going to be leaded around his play mates I always make a concious effort to let him get his play energy before hand and that is working very well at reducing his humping behaviour
In this case it maybe that hes using all his self control to behave calmly around children and the excited energy is showing itself in other (unfortunate) ways...
No idea if neutoring would help other than theoretically calming him down abit.
I dont think Dog on human humping is for sexual reasons (although Im sure someone will disagree) and so you might be better trying a good play session with him before he interacts with children to see if a fustration thing