Im actually just wondering what anyone else does in this situation. Totally minor example. We were at a bbq with family friends. They served some lovely, icing-laden cake for dessert. My DD (5) had one piece and asked if she could have some more. I said no, as she'd already had some chocolate that day and we're fairly strict on sugar usually.
Some of the other kids had more than one piece, which my DD wasn't happy about and kept pointing out that X and Y had had been allowed more cake and it wasn't fair. I can see her point, it wasnt fair, but equally, I don't want to give her the idea that I will cave on everything just because someones else's parent had a different opinion to me...I stuck to my guns for that reason (rather than the cake issue in itself!) but it did seem a bit unfair.
Same thing when we went to leave, some of the other families were staying later but my DD was exhausted after a busy few days (and it was an hour after she usually goes to bed, so I wasnt being that mean!)- but she couldn't understand why it was ok for them to stay, but not her...
What does anyone else do in this kind of situation? It's not like you can say "Well, soandso's mum clearly doesn't care that he gets diabetes/spend tomorrow totally exhausted... but that's why I said no to you...!" That isn't even the point, anyway...it's more if you make a decision, how do you stick to it even if other parents are doing sonething different?