I have never encouraged guns but even so my boys know what they are. They don't participate in imaginitive play with them between theirseleves but i have a nephew that comes over and he will find anything possible amongst our toy collection that he can use as a gun. I suspect playing with him is where my boys learnt a lot of what they know. Somehow i think a lot of it is just a boy thing

If they are playing in anyway that i find inapropriate i tell them and discourage the play. I would imagine you have tried this, i hope it's just stage