What is the average weight in stone of a 10-year-old girl?

It does really matter around height. If you are around 4 foot 6 to 5 foot, you should weigh:

4 foot 6: 4 stone 5 to 5 stone

4 foot 8: 5 stone to 6 stone

around 5 foot: at least 5 stone to 6 stone

Hope this helped and take notice :D