Rescuing Abandoned Kittens
Be sure the kittens are really abandoned before disturbing their nest!
The momcat may be nearby but hiding because you are there. If kittens are clean, plump, and sleeping quietly in a heap, they probably have a caring mom and should be left alone. Abandoned kittens will be dirty and the nest will be soiled. They will cry continuously because they are hungry.
If the momcat is friendly, leave the kittens with her until they are 5-6 weeks old. Whenever possible, play with the kittens to socialize them.
If the momcat is feral, remove the kittens at about 4 weeks. They will have received important antibodies from her milk. Kittens over 4 weeks old born from a feral mother become more and more difficult to tame. By 8 weeks old, the job can take months if it can be done at all.