What should you do you put your dwarf hamster in a ball to clean her cage and discovered a nest of babies how do you tell how old they are and what do you do now that you put her back in the cage?

It depends on a lot of things. If you touched the babies she might reject or kill the babies, so keep a close eye on her. As to how old they are, if there less than two weeks, they will be bald and blind, at two weeks they have a little bit of fur, and any older they'll have a coat and will look like proper little hamsters.