Do not blame yourself completely. From experience you cannot protect your "babies" all the time. Even if you had closed them early, perhaps it would have post poned this event. Often when we have preditors, its a matter of time. I went out of raising birds for a number of years due to a racoon pushing the glass out of the window, gaining access and taking out 5 goslings.
I was heart broke for years.
Raising birds is not for the faint of heart, but just remember, those babies had the best life they could have had with you. They had food, love and much more then a lot of them.
So, keep your chin up and know that I'm sooo sorry for your loss. Its hard to see past the anger, sorry . When you get so you can look up above it, build a better mouse trap and adopt some more babies.
Many blessings, take care and know we care.
~kel