I would have said no as well, but if we had out P and T one I would have given them the HC and used that if it was in the car or pram.

We did ask a waiter at a cafe when we were staying in Melbourne if we could use a highchair when the other family was finished with it, another family had an approximate 3-4 year old in it, and DD was only just 1, in the end we had food all over us and the chairs because DD wasn't very good at sitting on our laps or the seat and eating. Maybe it made them think to go and buy another!