Since it wasn't coming from the hallway and the bedroom doors were all closed, I went to investigate.
Someone (I suspect Sam), had opened the door to the master bedroom.
I could hear water running in the bathroom, and I came around the corner to find this:
When I asked what they were doing, Sam said happily, "We're having a party!"
Then Alex grinned at me and said, "We're dinking!"
Ahem, he means "drinking," but none of the boys can pronounce that yet.
Sure enough, one had a little medicine cup, one had a real cup and one had the cap from a bottle of hairspray. They were filling them at the sink and "dinking."
Sam wrapped it all up neatly, "We're having a dinking party!"
Great. They're two and already having drinking parties.
This, my friends, is why they invented the phrase, "If you can't beat them, join them."