The babies should be fine as far as heat goes at that age. How close to the old location did you place the nest? Have you tried talking to the cat's owner? I would trap the cat and send it to be adopted by someone else.

I am happy to report that by 6:45 this morning, both the mother and the father bird had found the nest's new location and were already feeding the four babies!!! Smart birds! I have a perfect view of the nest out my dining room window, and it is so funny to watch the bush around the nest quiver and shake when the babies are hungry and are making noise! I'm so pleased and now feel relieved that I did the right thing - the Mama and Papa bird have been working hard all day feeding those babies. (And as far as the cat goes, I'm not quite sure which crazy neighbor it belongs to - and unfortunately, I don't think either neighbor would listen to me if I talked to them about the cat (actually, cats - each lady has a bunch of them that roam around). All the dogs in the neighborhood do a good job of chasing them out of the backyards, but the front yards are still a problem...

I too found 4 Carolina wren babies on the ground in my backyard. I kept our dogs out of the yard for a couple days. I found them next to a wood pile and suspect the nest was somewhere among the logs. Just recently I've seen a cat roaming our neighborhood and found the remains of a rabbit on our front sidewalk.
Robin

I like watching birds and don't like to see them hurt, but why pick on cats? It's their nature to hunt small animals. They've been doing it for over thousands of years.

Aren't people more of threat to birds than cats anyway? With all the building that goes on, birds will probably become extinct one day. I live in what is supposed to be a rural area but it's like anytime a developer (or whoever) sees trees, they tear them down to build houses and stores. It's getting out of hand.

My personal rule is that I don't interfere with nature. I would've left the nest alone. If birds are that stupid to build nests where predators can get to them then they deserve whatever they get.

Around here dogs are the biggest threat to birds. Several of the neighborhood dogs have a bad habit of killing small animals. One of them even ate my father's rooster! The only birds my cat has killed is those annoying Blue Jays who were just asking for it. Those cocky things fly around teasing the cat so when one gets eaten I don't feel sorry for it. Stupid birds.

are the blue jays teasing it or trying to protect fledglings or a nest? just wondering...

but anyway, i'm so happy your wrens caught on! it would have been a shame for them to get nabbed by a predator, cat or otherwise. at least now they have a little more protection

If people import and introduce problems into the ecosystem-dogs, cats, rats, House Sparrows, pesticides, etc, these things are not "nature." A bobcat hunting a Carolina Wren is nature, not some non-native domestic housecat released on the wildlife by an irresponsible owner. Humans have a responsibility to clean up their messes. If you can trap the cat that would be great.

People aren't nature either. Guess we better invest in bigger traps. And lots of them.