From the title, I thought you'd found your kids sitting on their own in front of a locked up house thumbing lifts....
If your three year old and five year old are anything like mine, then getting on coats can easily take ten minutes chat. Presumably everyone was tired and wanted to wind up the day as efficiently as possible.
In my culture, kids with coats indoors are a no no. The thinking is they'll get hot and sweaty being overwrapped indoors, and then catch a chill when they go out. I would have been more p'ed to find them muffled up and uncomfortable indoors while the CM did her own thing.
To me, she sounds pretty caring, tbh, to sit with them and wait, even when 'the meter had run out'. Have you thought that maybe your five year old saw all the other kids being picked up - or even looked at the time - and started to get upset that you weren't there? Getting dressed might have been an effective distraction from sitting on the bottom step worrying about whether you'd forgotten. since you hadn't phoned, the CM would reasonably expect you to be there in minutes not hours.
When my Dd was at nursery, me and another mum were always cutting it to the wire, picking up at six on the dot. I swear, 5.55 penultimate child, Dd was happily playing. However, if the other mum had pipped me to the post, and it was 5.59 and Dd was the last one, I'd always find her sitting like a little orphan, big sad eyes, holding the key workers hand.