If they are fledglings and are fully feathered they do not require a heating pad, they can stay at room temperature(75 degrees) . Instead of using egg shells use a tums tablet, any flavor that has been dissolved in a bit of water, With egg shells the exact amount of calcium is not known. mix that with 1 cup of dog/cat food soaked, get dog/cat food that is the closest between 33% protein and 12% fat, 1 hard boiled egg mashed in and 1/4 cup of applesauce, I just get the small baby food jars, their is exactly 1/4 cup. The consistency should be like cooked oatmeal. Of course only do this if you HAVE to save a baby bird. Robins are protected by law so they have to go to a rehabber. I usually take all the illegal birds to a rehabber and keep the pigeons, house sparrows and the starlings. I have my starling sitting on my arm as I type this. I have had tons of babies fall out of the nest around here and my cat stalks them but I just put them as high as possible in the tree. The parents will freak out if you touch it! I've had one swoop at me. "Mom will smell you if they are touched" is a total myth like everyone said. Do not go buy handfeeding formula at the store this is not for songbirds, songbirds are insectivores and that was made just for parrots. NEVER give earth worms to a baby bird, it can cause gapeworm. Although they do feed them in the wild, you should not. Mealworms are all fat and like candy so they can be an occasional treat. I would just stick with the dog food mixture. You can buy crickets and use them as a treat also. Do not give them water, they get all the moisture from the mash recipe. At 4 weeks for can give them a plate of water. Good Luck with whatever you decide but keeping them is a huge commitment and they have to be fed around the clock. I start feeding at 5:30- 6:00 Am, and stop around 10:00 PM.