"Lullaby" by Billy Joel used to work for DD... I used to get a bit teary singing it to her too Such pretty lyrics... "Goodnight my angel time to go to sleep, and save these questions for another day..." but the bit that always gets me is this bit:

I promised I would never leave you
And you should always know
Where ever you may go
No matter where you are
I never will be far away

Or "Goodnight sweetheart" from Three Men and a Little Lady, not sure if that's the right name for it but you know the one!