Why did our friends insist we come to their tailgate party if it was a kiddie-fest. We don't have kids?

My husband and I got an invitation to a tailgate party at Saturday's football game to our friends who have 2 children. They said they weren't able to get a sitter and they had invited several other families from their neighborhood to join us. We tried to decline-we preferred to do our own thing-but they insisted. When we got there, they totally ignored us and just talked to the other families about what the kids were doing. Not great fodder for a pre-game, beer drinking activity and hubby and I were totally bored. We have always done their kid activities with them in support of them having children-showers, bdays, etc- even though we do not (at first it was health reasons we don't, and now we've just decided it's best this way) in the past, but this is not one of those times. We were good sports and contributed to the conversation when we could. Was it rude of them not to talk to us about stuff that interested us too?