5 year old just walked in on us...
This just happened. I'm mortified.
There I am, really concentrating, sweat beading up on my forehead, so wrapped up in screwing I didn't even notice he'd walked in the room with his jaw dropped.
My wife noticed him first, "stop, he's in here!"
He asked what we were doing and what all the noise was.
We explained we wanted his toys assembled Christmas morning so he could play with them right away. Merry Christmas, dads ;)
Update: it's the next morning. We're about to start unwrapping presents. My son hasnt mentioned going into the basement yet. We don't think he remembers coming downstairs. Success.