What's happening in your world?

['thul]

Oh, a bit of flour wouldn't ruin the clothes... it'd just leave them in need of washing, and that is not practical every time baking is done. Clothes should be washed when dirty, not after baking.

These beings would probably be able to figure out where to buy an apron fairly easily where they live. There's a couple of stores that sell their own portions of everything. If neither of those has an apron, it'd be strange. (and if the need was great and availability lacking, one could always buy a bed sheet and improvise)