"Kittens old enough to be spayed or neutered and too old to be socialized can be trapped with their mother, neutered and returned, but younger kittens, with or without their mother, present a lot of options, most of which involve fostering and sometimes a great amount of care.
Kittens can be socialized and adopted, even if their mother is feral, so they aren’t necessarily returned on the basis of their mother’s behavior."

Additionally, the best age to socialize kittens is 4 - 8 weeks, and leaving them with their mother where they were found also risks missing the window when the kittens can be socialized and not have to live out their lives as ferals. Of course, if the mother is friendly - and space available - the entire family can be rescued and fostered. If mom is not friendly, the decision is difficult.

"Kittens younger than eight weeks are best living with their mother even if she is feral, but do you leave them there knowing the mother will likely move them, and hope to find them when they are eight weeks and ready for surgeries, or do you somehow foster a feral mother while socializing her kittens?"