My DS' party last week. I didn't have time to collect preferences for meals because I organised the party 10 days in advance and the swimming pool needed to know 7 days before the party. So I gave the invitations to my DS to hand to his friends at school and I didn't enquire into vegetarian or other dietary restrictions. I simply arranged for all the children to have a hot dog. I assumed the parents would tell me if their children were vegetarian at the time of letting me know I'd they were coming.
Turns out one little girl was vegetarian and I felt awful she could not have the food.