Try something simple with them, maybe you'll have luck like I did. Put the babies in a breeding net with some live plants in it, usually
Anacharis is good, it's viney and easy to place in there floating or stuck in the sides(I do a tangle of both, they can get around in it fine and hide), add in a little piece of algae for them to eat, a very small piece, and just leave it in there overnight with the lights out(You have to change out a little of the water in the breeder everyday, though you should anyways, even if it has good waterflow in it when you do that, but they get what they need and I haven't seen cories over-eat before, but watch out for it anyways). I find babies need to have food when they want it, and A LOT of hiding places to feel properly secure, otherwise they can see the adult fish but can't get away and this stresses them out. Maybe it's something as simple as that, afterall, they live fine without too much butting in usually. Or you could move the parents and leave the eggs be in the original tank for a week or two. Sometimes it's easier to just move the parents instead of messing with the babies. lol
You can't really keep sand in the breeders...but if you get the net kind they should be fine without hurting their delicate barbels and bellies for a week or two, whenever they're big enough to be with adults. Since I started planting my nets or using the nursery tank(A ten gallon for birthing mothers and babies to grow up in with a lot of plants and hiding caves), I haven't lost any babies. Sometimes with new babies or delicate eggs, it's all about moving them, and the less you have to do so, the better their chances. Although cory eggs don't always give you a choice, especially when they lay them on the heater. ^^;