Casual dress

Yesterday I was so, so tired all day long.  Maybe that's why I laughed so hard when this conversation ensued:

Scene: I'm getting the twins ready for bed.  My darling little 2 1/2 year-olds who we still refer to as "the babies" around here.  Gotta stop that soon, I guess.  We've been working on getting the twins fairly independent with dressing/undressing.  Isaac is struggling with his undershirt, so I help him pull out one arm, but then he proceeds to pull his arm out through the neck hole.

Me: "Isaac, sweetie, not through that hole.  Through the bottom."
Isaac: "This is the bottom?", pulling his arm out the right way.
Me: "Yep, that's the bottom!"
Isaac, pointing to the neck of the shirt: "And this is the **** (male part)!" Said confidently like he just figured everything out.