Metal BBs can be hazardous, in a sense that if you shoot them it may break the skin. But airsoft guns use platic BBs, they sting, but don't break the skin unless you are like 2 feet away and even then its just a scratch. So, yes, they are safe(assuming you don't get shot in the eye, ouch
always wear a mask or goggles)
Contradictory to what I said before, be careful if you are handling an airsoft gun with roughly 400 fps(feet per second) or higher, because those things are serious and really can cause some damage. but most guns are between 180 and 350.