I've never met a normal five year old that has not at some point in their life simulated a gun with their finger or made a gun out of a broom stick, Legos, Tinker Toys, or something else. It almost seems to be a natural thing for them to do, and this includes kids raised in fervent anti-gun households.
gun- well, we all know that is too dangerous for children to spell
sun- that can cause cancer, so we don't want to promote that either
bun- way too sexual for a five year old!
nun- we can't be discussing religion in public schools
run- that is not allowed in the hallways!
I guess that leaves fun and pun...good luck getting a five year old to draw a picture of those!