Yes, it is legal and in fact they must under PACe record him.
They are not going to tell you anything over the phone for two reasons. Firstly that would border on an interview which is unlawful save for under tape recording. Secondly some people would use the information to start concealing evidence.
If he is under 17 then they will need an appropriate adult to interview him but unless he attends the interview they will just come and arrest him. They don't like to do that because it is labour intensive but it is the only option with people who won't attend voluntarily. Can I clarify anything for you? Jo