Apology Letter For Waking the Baby
Dear {Recipient},
I'm sorry for waking the baby {last night/this afternoon/etc.}. I know how difficult it can be sometimes to get the little one to sleep; I feel so bad for undoing your efforts. I should've {kept my voice down/noticed the squeaky toy on the floor/etc.}.
I hope you were able to put the baby back to sleep without a hitch. I will be more {quiet/careful} when I'm around {him/her} next time.
Sincerely,
{Your Name}