I would follow the advice give by TFOX. That said, if your bow is generating at least 55 ft/lbs of energy, any you are able to shoot bullet holes through paper at 3, 8, and 15 feet, mechanicals can be deadly. Keep the heads to 2 or 3 blades, and cutting diameter to no more than 1 1/2" and you should be fine shooting mechanical heads on deer size game.

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