Ermm this is a tricky one!
One question I need to ask is, does your DD go to PreSchool in the school hols, would you expect your childminder to look after her?
In one way you shouldn't be charged as you drop her off, that way the childminder becomes responsible for her from 12pm, so no charge, but if you want your DD to go to her from 8am to 12pm in the school hols then the childminder could charge to keep those hours free for you i n the school hols - otherwise the childminder may fill those hours and you would have no one to look after her in the school hols - does that help at all!