I've had an arrangement with a mum at school recently where she kindly drops dds 2 and 3 at home while I am taking dd1 to a ballet rehearsal. My cleaner comes for a few hours to watch them until dd1 and I get home. My cleaner has a key and lets herself in around half an hour before they are brought home.
Last week I had a call from my neighbour to say that dds 2 and 3 were with her as when they were dropped home, the cleaner hadn't arrived yet (it turned out she missed her bus and was really worried about the girls). Luckily dd2 has the good sense to go to a good neighbour and luckily she was in.
But I'm cross that the mum didn't wait until they were safely inside before driving off. I asked dd2 and she said she waited while they rang the doorbell.
Dds 2 and 3 are 9 and 5 btw. I would wait for ANYONE to go inside safely, adult or child.