Took DS to a young child's birthday party at soft play today, and there was a vegan mum with her DC there. When it came to cake time, there was no vegan cake, so the mum gave her DC a chocolate lollipop out of her bag.
OK, her DC seemed happy with the situation and asked to hosts to check what was and wasn't vegan. So no problem there I don't think (although I'll bet my bottom dollar they'll rebel and live on bacon sandwiches when they're old enough to ignore their mum!) 
BUT AIBU to think that taking separate treats to a party is A) rude to the hosts and B) unfair to the other children at the party who might prefer what the vegan DC are eating?