When I was pregnant with my first child, God gave me this little lullaby to sing over him.  Many early morning hours were filled with this song- adding in many more verses including, Daddy, Grandma, Grandpa, etc... and many more hymns and praise songs.   Kids are much more forgiving than big people;).  They really don't care how you sound, but they will remember the words that you sang, and the love behind them.   Songs fill their heads and their hearts for an eternity...  Sing away!