Just curious....if you invite your child's friend to a movie or skating or anything. Do you expect money from their parents? I fully expect to pay when I invite someone to soemthibg but I will take extra money in case the child wants something extra.
I do however find it odd when the parents don't offer money. It's just the nice thing to do. I always make sure to offer or send money with my kids when they are invited soemwhere.