You should make sure your child does not get your phone and buy. They are very clever as they have to go through two screens to buy.
You have no automatic right of cancellation unless it is a business in the Uk
You send a cancellation request but the seller does not have to accept it
Buying and then wanting to cancel wrecks their listing and will lose them money
I a assuming the child did not pay too?
See the link on how to send a request
https://www.ebay.co.uk/help/buying/cancelling-order/cancel-order?id=4004#section1
If you dont pay then they can open a non payment dispute and once closed you get a non payment strike on your account
