Airsoft guns don't have enough 'oomph' to kill a bird - or any animal. Are you sure they're not using BB's?
Airsoft gun's - a lot of the talk here, I'm wondering if the poster's are talking about BB's.
My son had one (he just asked about it this afternoon - I have no clue where that thing is

) and played with his friends, with it (they all had them)
I was worried about them - my son was about your son's age when he got it. So, I told him to shoot me with it. It stung - like if someone popped a rubber band at you - but it didn't *hurt*. It was more like 'ouch!' that went away instantly - not OWWWWWUCH! leaving any sort of mark.
Most of the one's they make now, are very obviously not real guns. Heck - one of the boys had a hot pink one.
With rules - I don't think it's a big deal, but that's just MHO.