Sorry been out for a while, yes most likely Social Services- although if the child is not known to them they may or may not attend. Whatever happens, try to stay calm, assertive in his innocence without being confrontational.
If I were them, I'd get a solicitor if at all possible to advise them far better than I can, but even if they don't charge him there and then they are likely to question him under caution so he'd need some legal advice, and then most probably bail him.
the alternative to the horror story scenario we've painted is they genuinely just want a chat with him, but I doubt it having seen the way the police treat teenage lads from the ones I mentor.