Welcome to the forum!
Glad you joined us, just wish it were under better circumstances.
Eight 4 week olds all gone without a trace and the door ripped open. Probably happened overnight. That eliminates some things, but there is still a pretty good list of possible suspects.
I have had a hen come back the next morning after a dog attack in mid-afternoon. I have no idea where she spent the night, but she was wanting back with her buddies the next morning. From what you describe, I would not hold out much hope, but there is a possibility. If it happened at night, they probably could not see to get to safety. I wish I could be more positive.
Them being only 4 weeks old makes it a little harder. They are still small enough that something could eat them without a trace where with larger chickens there would probably be traces. I hate raccoons and they are a possibility, but I think a raccoon would probably eat them on the spot or at least not carry them that far. And I would not expect them to eat all 8, even at that size, though they could kill them. Not all predators read the book and act typical for their species, but we are only guessing.
I don't think a snake would eat that many, plus a snake might have trouble ripping the door open. That depends on how strong the door was and how big the snake was.
Some member of the weasel family like maybe a mink could do it, but I think they would leave evidence. I don't know how likely a wolverine or bear are where you live. Those might be a bit exotic. I'm not sure how a bobcat would act. I don't know their traits.
My real suspects are dog, coyote, or fox. Any of those are capable of eating them or carryiing them off for later and they are pretty strong. It is possible something else took them back to their cubs, kits, or something too. It's early in the year many places, but maybe some of them have babies to feed.
This is real hard, especially with the child. I really am sorry this happened.
a lot of Mommas are eating hard right now getting ready to have kits I have been keeping an eye on a pair of yotes and she has not delivered yet