to let 6yo ds1 go out and play wearing only a pair of wellies?

[everGreensleeves]

he asked if he could go out and play with nothing on, I said "no, you'll hurt your feet", he replied "well what about if I just put my boots on"......and I couldn't think of a reason to refuse

will the neighbours think we are completely out to lunch?

No, because of the sun. But then I live in NZ so I would insist on wellies and a sun hat.

Another YES vote and of the weather

yanbu