I have a similar dilemma here, @Celia60 , and have handled it by toggling "not suitable for ages 0 to 12". Then in my house rules I have a line about "older children who are used to camping", with a note to ask me at the time of booking.
What happens is that people tick the box that says child, and suddenly they cannot instant book, but they can send a request. They tell me how much their 10-year-old loves camping, and I say yes, and then they are able to book and show up.
It works well. Sure, I would rather be able to choose more specific ages, but I have had no trouble with honest guests.
The dishonest guests are not stopped by anything we can toggle anyway. 🙂