DSS's mum is erratic, with bursts of volatile behaviour. DSS is hugely protective of his mum and stays with her most of the time, stays with DH and I, when he wants. Used to be EOW, but that is now pretty flexible as he's a teen. He is welcome in our/his home as much/little as he wants.
Recent the erratic behaviour has been getting more frequent and intense, with DH getting called by DSS asking to be collected from his mums because she's drunk, they've been arguing etc. He'll come and stay with us, but ultimately leaves after 1-2 days because he's worried or because she's begged him to come back.
Last night DH got called by DSS to collect him, clearly distressed. DH had to leave his Christmas party and I drove to collect DSS. He later admitted that his mum had punched him. He doesn’t have any visible marks, but is obviously distressed. DH has explained that he needs to stay with us for now. But he is just desperate to get back to his mum. My first instinct is to report it. Is that the right thing to do?