Had a horrible breeding cycle this week. 2 does kindled, Cally and Cookie. Cookie was late, & had a single, large, partially formed stillborn kit. Cally had a litter of 7, but absolutely did not like the new nest boxes I had built. (old ones were just a wood open top box, chewed to crap and disgusting.) She kept pulling the nest out every time I would refill the box, until finally, she decided to have the whole litter on the wire. When I found them, they were all over the floor, (the value of baby saver really got drilled in) 3 were already dead, but 4 revived after a while in my shirt. I put them in the nest box, and placed the box in with their mother... after watching a while, and several checks, they didn't appear fed. I put them in Cookies cage and she jumped right in and nursed them. Cookie got the litter.
2 of the 4 kits have died since, yesterday, and another today. I am warming the remaining 2 in my shirt again, but I know 2 is too few for them to stay warm, so the box is coming inside. So, finally, the question.

What temp would be best to keep the house at for the kits? I usually keep it 60 in the house.. but the garage where the buns are is only about 12 deg cooler right now. How much heat would be too much?

60 might be a bit low in their current condition. At 66-70F my singleton and 2 kit litters always did fine in the house with just a little fur and were usually trying to wander off by a week old. That doe never had more than 3.

They need to be warm and fed (in that order) first though or it won't matter. If they have no milk to digest or are too cold to digest it (could be what happened to the other 2) they will produce hardly any heat and will not stay warm without an external source. The body temp of a rabbit is over 100F so even in your shirt you are barely getting them warm enough to be alive and not to eat and digest well. You can give them a hot water bottle for now. A plastic container filled with hot water and wrapped in a cloth or anything else that holds warm water or those heatable cold/hot packs works just fine to get them up to temp and keep them there. If you've got an extra thermometer (not the medical short term temp taking ones) put it in there to make sure you don't go over 103F. Our tapwater can come out above 105F (I think 110 but the meat thermometer isn't the most accurate) so I've had to be careful sometimes even when I don't heat the water. Microwaving will make it even more likely to get too hot. A heating pad or electric blanket can work but don't over do it and don't put it under or around the whole box so they can leave if it gets too warm. Again a thermometer is a good idea.

Once they are warm and then the doe has fed them well they should be ok in the house, probably even at 60F since you will be heating them the first day or 2 and they will be older by then, if you keep them close together with plenty of material for warmth. Make sure they have a little hole/indent that keeps them from wandering away from each other and I would pack the box with straw or hay around them in their fur. You can also add dryer lint or fleece bits for less mess or if there isn't a lot of fur.

Thanks Akane, Excellent info and reference points.I will definitely kick the temp in here up a bit. Very good info, that I'll keep in mind if this ever happens again in the future. I was trying for fed instead of making them warm as possible. I was somewhat on the same page though, figuring the milk would fuel their warmth. Right now they are inside in their nest box with plenty of hay and fur. I have a 40 watt drop light shining on part of the box as well, and feel less apprehensive about having it there knowing they should be up toward 100.

I had actually been debating earlier whether to just bring all next boxes inside for the first few days during the winter. Figuring the kits could spend their food energy growing rather than keeping warm. I think I am leaning that direction after this. These are only my 6th litter, so I have plenty of learning the ropes still to do.

There are nestbox heating pads available from rabbit supply companies. I have one on hand in case of need. After the first couple of days they are usually no longer needed, but with a small litter like that you might use it for a few days at least. If you have a power source where your rabbits are kept, it might be more convenient to leave the nest outside with the pad.

Sorry to hear of all your losses- I hope the two survivors do okay!

Thanks MamaDheepdog, they're in an attached garage, so its only about a 10 foot walk. I haven't been too concerned about the temps in there so far, as even when its below freezing outside, its in the 40's in the garage. Right now, my phone says its 33 outside, and I am showing 48 in the garage. If I get them something set up outside, a heater might be a consideration.

Hopefully these 2 will get over the hump, and I have learned pricey lessons. Both does did great with their last litters, both seem as big as the rex litter that was 2 weeks older. Cally had 5 and raised 4 (nursing mishap I assume, and the kit crawled directly under the J feeder where I couldn't see it) and Cookie had and raised 6. I guess I have to make Cally an open topped nest box instead of the covered design. I can understand Cookie's failed litter, but losing 5/7 of a good litter for not good reason just stings. =)

you can make a makeshift incubator---works really well with old fish tanks.

You need two fish r=tanks, one a bit larger than the other, aheating pad that will not time off, a small container to hold water, and thermometer some towels..

place the heating pad in the bottom of the larger tank. place smaller tank on topof that, and line with towels. place a container of water in the inner tank, directly on the glass, so it warms nicely. place thermometer inside inner tank, put babies in
nest in inner tank, cover the whole thing with another towel, and monitor temps tomakesure it remains steady ant the desird temp.
the water dish provides humidity, when the kits start moving, place the the dish in the larger tank.

I have a seed starter heat mat that does very well for me-- it is a bit more reliable, and provides a more even heat source than a heating pad-- also a bit safer, as it is moisture resistant.