How old is the kitten? Ideally kittens should stay with their mums until they are 8-12 weeks...but with ferals I'd take them at 6weeks, before mum teaches them people are bad. If you're really worried that the kitten is in danger I'd try to either bring mum and kitten in, keeping them in a bathroom/spare room, or bring the kitten in if it's in immediate danger.
I have made this choice myself. When Muffin was about 3 1/2-4 weeks old his mum started taking him on walks around the area. (His mum was feral and in the colony I was trying to take care of) A mean neighbor told me if he caught any kittens he would kill them. I brought Muffin in that night, and he hasn't ever left.
It would be best to try and get mum-cat inside too (using a carrier with her kitten inside to catch her), but if there's no way to do that then you need to weigh the risks. Keep in mind that if you separate them it will be your job to raise the kitten, not just feeding but teaching it manners too.
Don't worry about having to tame the kitten of its under 5-6 weeks. Especially if you've had contact with it before. Muffin was 'wild' when I brought him in, it took 5 minutes some food and snuggles to convince him I was nice. That's a bonus to getting them young, but there is a LOT of work involved too.