Should I be a "helpful" neighbour or should I keep my nose out and ume annonimity?

My neighbours three children (all about 3.. poss. triplets) were out on the street this morning. They had decided to run down to the busy main road at the end of their cul de sac. I went over to try and get them to go home but (short version) they wouldn't go. One had a full nappy falling off. they started playing a game of chasey in the direction of the road. another neighbour (who is a police woman) came out and chased the kids (around the block) while I woke their mother (1 minute politely knocking on the front door). The kids are often on the street without supervision. The police woman has said she is going to call family services and report the mother. The kids usually escape from the back gate which they can obviously open, and although one had his nappy falling off they were in relatively clean clothes and are obviously well fed. I want to take a sliding lock over to the neighbour and suggest she put it on the gate so the kids can't get out without her knowing. I don't think she is necessarily a bad mother, just young and poor. My husband thinks I should keep my nose out of it and the police woman thinks I should report her too... what do you think I should do?