If it were my son I would up the broadhead wieght to 100 grns, and he would be shooting the Magnus stinger. I believe it to be the very best broadhead for lower energy setups. I don't have a problem at all with taking your son to a range or preserve. That is provided they run a quality operation with a decent amount of property to hunt. In fact I sounds like an excellent idea. Just curious how old is your son, and at what age is he legaly able to hunt NY.
With a 40lb bow of modern make, with properly tuned and matched arrows and broadheads he should be able to hunt deer size game if the shots are limited to 25 yards or less.

TAKE YOUR KIDS HUNTING AND YOU WON'T BE HUNTING FOR YOUR KIDS