It should have been stipulated on the invitation. You can’t expect the parents to know what you want unless you tell them. I have 3 children and thankfully they have only been invited to two parties where the hosts wanted parents to stay and both were stipulated on the invitation. All the other parties, including the ones I have hosted for my children, have been 12 or less guests and no parents. I think it’s crazy to invite 31 kids to a party when most of them won’t actually be friends anyway and I wouldn’t want my kids to get caught up in the consumerism of 31 presents! 31 invites in my eyes would be reserved for an 18th or 21st birthday.