Kids will always be kids anyways. It is common among kids to fight over things like phone. It is now at your discretion to know the limit you can go with anything concerning phone to children. It is good they apologised but still use your description to know if you will give them back or not or better still, be the one to hold the phone while they watch it. But to be frank, you have a very soft spot for kids and that is quite commendable.