Hens can hold the seed from one mating session for a period of time to be used to fertilize future eggs. I don't remember how long that time might be, but it is possible these are your rooster's chicks. The hen takes time to build her clutch before setting, laying one egg a day until she gets her magic number. Then they all begin to develop at the same time once she begins to set all day long on them.
So perhaps these chicks are from the first few eggs she laid, which may have still been fertile from her last coupling with your roo, but the rest of the eggs she laid were infertile. So these could be the only chicks that hatched, and she made a heroic effort to bring them to safety.
Do supply them with chick starter to eat, even the hen can eat it while she's tending her chicks. And certainly give them water, in a drinking fount if you have one. Chicks start eating & drinking as soon as they leave the nest, usually the day after they hatch.
I hope they are the hens you want, but go ahead & make plans for their future in case they're roos.