Thank you Christine. Life intervened last week in a way which rather made my previous worries pale. On the Thursday morning I looked out when I was waiting on transport (my son is taxied to his special school, my daughter is bussed to hers) to see a strange collie cross squatting on my front lawn. I went out to see if I could see an owner as ours is a quiet street but it's not typical to see dogs off lead with no owner near at all.
A middle aged man was puffing up the street and apologetically waving his lead and shouting. He put the dog on the lead and said to me that she'd escaped round the front door twice that week, "no' like her". Off they went and the bus arrived and I went to organise my daughter onto it.
Later that day I was walking my two and they stopped and planted their feet and drooled over the front lawn on the way out and the way back, and I thought a-ha well THAT'S why she's escaping! She must smell extra lovely.
That night I was out with friends and my husband was left in charge. The next morning when I got up he told me that the previous evening he was putting our son to bed when he heard several shouts of "hello, hello" downstairs and went down to find the front door wide open and 2 strangers stood in the hall. The dogs had seen a similar dog (not the same one I don't think) go past the window, the 16mo had opened the front door and the two of them had gone off after it. The strangers in the hall live on the street at the end of ours and recognised them as they went by but couldn't catch them so began going door to door looking for an owner. They eventually got my husband who had to leave a neighbour we barely know and my 12yo who has autism herself in charge of the other kids and go after them. When he found them they were on the grass verge of the bypass

. Unharmed by some miracle. Ironically they recalled immediately and joyfully on his first shout.
That rather galvanised us all. I had to sit down when he was telling me. I felt sick! If we didn't have such kind neighbours they wouldn't have needed neutering, being as they would have been, squashed flat on the bypass.
I dropped them off on Monday morning and when I was waiting for them to be taken in the eldest drooled a pint of dribble onto a spot on the floor where some bitch had been sitting which he sniffed dreamily with dribble pouring out. The staff were all in the waiting room discussing a "silent" season as an owner had a bitch he said had only been bleeding 2 days but had been bred by a random dog on her walk that morning. The fairly junior vet who'd seen them had come out to confer and they were all discussing how first seasons can be atypical and saying it can't be the 2nd day if she stood to be bred and debating injection/spay. And when I got in my car who should come out behind me but the man with the collie on my lawn!