rock-a-bye-happy-birthday

Derek favorite song he sings to the girls:

1st verse:

Rock-a-bye baby, in the treetop
When the wind blows, the cradle will rock
When the bough breaks, the cradle will fall
And down will come baby, cradle and all

2nd verse:

same as the first except it's hummed which is then morphed into:

Happy Birthday to You

Happy Birthday to You
Happy Birthday Dear (Amelia or Emma)
Happy Birthday to You.

Not sure how it happens, but it does every time. And it usually ends with me saying

ummm...are you humming happy birthday?