Vicki, looking for a babysitter - LL55 Beddgelert

We're getting married at Llyn Gwynant Campsite on 25 July. We don't have children but a lot of our guests do and we'd love to arrange a safe, supervised area for parents to be able to leave their children during the day. We'll set up the space with toys, games, etc, and we are looking for childcare professionals to supervise the children in that space from 2pm - 9pm.
Happy to take guidance on how many childcare professionals are required for this. There will be 20-25 children, mostly toddlers.
I expect parents will come and go throughout the day so its unlikely that there would ever be more than 20 children at any one time (though it's hard to say for sure).