When they have just been born, they still have their egg tooth in their mouths and the yolk sac hanging out of their bellies. The egg tooth is what enabled them to open the eggshell, it will fall out on its own. The yolk sac is what fed them while they were incubating. DO NOT try to remove this sac, trying to remove it can kill the baby turtle. It is better to wait till it is absorbed on its own. Once it is absorbed, you will notice a split in the plastron. This will heal by itself too, you don't need to treat it.
Set them on a 20 gallon tank per dozen turtles . Provide them with a dry land area and a shallow water area. Newborns need to master the art of floating and staying underwater for long periods of time. Don't assume that they will survive only with water. Newborn Red-Ear sliders can actually drown if you neglect them a dry land area. The water should be not too deep. As with adult sliders, newborns need to have their full spectrum light. So don't forget to include that in the tank. The full spectrum light will help the newborn shells to harden. Keep the water neatly clean. If you don't have a filter change the water every two days. This is very important since baby sliders are more prone to getting eye infections (that can leave them blind for life or even kill them) than adult sliders.
Once they are set up in their tank start feeding them. It is important to get them to eat. Start by offering them one by one all items on the proper slider diet (earthworms, crickets, sweet water shrimp, aquatic snails, water hyacinths, fruits, one commercial food). Note: You might have to 'chop' all of the food you offer since they are small babies. This includes chopping earthworms, meal worms, crickets. I know, this sounds disgusting but believe me, you will get used to after a while and it won't bother you anymore.
A Baby That Refuses to Eat:
If you have already tried all items of a proper Red-Ear slider diet, and the hatchling still refuses to eat, try offering a small piece of lean beef or ham. This is just for the purpose of turning on his appetite, once he starts eating you can try again to give him the items of a proper diet. If a week has gone by and the hatchling still refuses to it, you will have to force him to eat. Make a solution of beef blood and turtle vitamins and using a drop dispenser get the drops in between his lips.
How to Prevent Most Common Diseases in Slider Hatchlings:
Keep the water neatly clean, provide him with a full spectrum light, keep him warm (about 80 degrees), and add vitamin supplements to his diet. Make sure the supplements are high in vitamin A and calcium.
The most common problem in slider hatchlings are eye infections. These infections develop due to dirty water and lack of vitamin A. The treatment is easy: Change the water more often (get a filter if you can), add higher doses of vitamin A to her diet. Ask your pharmacist to prepare you a solution of 97% distilled water and 3% boric acid. Clean the turtles eyes with this solution twice a day. If the eyes are totally closed, try to open them so that the solution gets inside. Raise temperature at 85 degrees F. If the infection is severe take the turtle to a vet since she will need to be injected with vitamin A.
If you notice your turtle has a runny nose, or is breathing with her mouth open, she might have a cold. Avoid breezes and cold drafts of air. Raise temperature at about 85 degrees and add extra vitamins to her regular food. If she doesn't seem to get better in a couple of days or you notice that she is swimming lopsided, take her immediately to a veterinarian! she might have developed pneumonia which can be fatal. She will need to be treated with antibiotics.
Information provided by Reslider's Swamp