On one level, this isn't surprising. The party, after all, is being held in their house. They've tactfully gone out to see a film or have a meal. They've hung around on the street corner in the rain, wondering if it's too early to go back. And then, at 11pm, they've skulked up their own front path and put the key in the door.
But usually, in the past, all they did was tiptoe upstairs, bravely ignoring the muddy footprints, the crushed crisps in the carpet and the spreading stain on the sofa.
"Her dad started offering us all drinks," said my daughter the next day.
"What kind of drinks?"
"Beer, I think," said my daughter. "But everyone was too embarrassed to say yes. People started saying, oh, I think I'll go now'."
My friend's daughter tells me that her mum once came back at midnight from her own night out, threw herself into the party spirit and ended up dancing on the kitchen table.
"What did everyone think?" I ask, breathless.
"They were quite impressed," she says.
The trouble is that no one ever feels older inside. All the signs of miserable aging are there for everyone to see. But on the inside parents still feel like teenagers themselves.
"So next time you have people over," I say to my daughter, "shall I get out all my old 45s and run the disco?"
"Ha, ha," says my daughter. "Very funny."
Do you enjoy crashing your children's social life?