Once upon a time, children freely discussed all of the latest toy weaponry they were collecting, but times are very different now: A Bronx elementary school was placed on lockdown this morning at the mere mention of a firearm, only to be lifted when a police search turned up nothing — the kid in question meant his Nerf gun, which shoots foam darts and was at home. But if a small child with a gun at school sounds crazy in the first place, it’s just not.