yeah they are foam golfs balls that are made for practicing (Target sells them). they are just the right density that they add weight, hard enough that i just drill a 1/4" hole about half way through them and push them on the arrows, but soft enough that they are safe. of course we don't shoot at anything we're not supposed to, but they are kids after all.
i used to set stuffed animals up around the house and we would go on "safaris", but they are getting stronger and even the foam balls can cause damage in the house!