Raising babies can be very rewarding but heart breaking also. I have now raised a few hundred very successfully but most likely lost an equal amount. Sometimes there are no apparent reasons, some times it is a genetic problem. I have raised some to six months old to all of a sudden lose them 1 by 1 with no apparent cause, diet, water, temp, ect all the same, they just started dying. They didnt even show any physical signs such as floating or fungus, it happens.
If i could give some advice it would be this;-
Only have about 6 babies to each container (plastic take away tubs are ideal)
Only use newly hatched brine shrimp or daphnia and rinse well in clean dechlorinated water. (Remove dead food as you see it)
Try to maintain a temperature below 16 deg the cooler the better.
Do water changes 1/2 times daily with dechlorinated water the same temp as your babies are in.
A small piece of plant life will give cover if you feel the need but as long as the containers are kept cool and out of the light they should be fine, I cover mine with a cloth.
This is all you can do at this early stage and the rest is in mother natures hands.