Next door neighbours were round for lunch last weekend and said they were in need of a childminder for their 12yo the following weekend. They were off on a weekend break and their childminder fell through. We offered (it was no problem really - we have a 2yo ds who loves the attention).
In the end the mother didn't go on the holiday (hay fever attack) but the 12yo still came round and has been staying with us for two nights, while her mother is next door, perfectly recovered from hay fever.
We haven't said anything, as we're too polite and perplexed. So AIBU to think they should have stopped their daughter from coming over and the whole situation is weird?!?