So if you opened at 6 you'd be happy to let them in?!

Your opening hours are irrelevant to parents that aren't using it to be honest, as far as this contract is concerned, you don't start work till 8am, and so, particularly as you were in bed anyway, you weren't open for business at 7am as noone was due.

Having read that it was actually a nanny that dropped off, had she been made aware that you aren't contracted till 8am by the parents, or had they ok'd her to drop off an hour early?

It's not about being brave, it's about sticking to contracted hours....