Wish I lived closer to you! I *bleep* up kittens pretty quick! LOL! That's how we got the last few!
As others have said, putting out food helps. Sitting nearby helps, but not as quietly as you think! You need to talk to them a little, in a soft voice. Get them used to the way you sound. If you don't, they may just run off.
Another idea is to make a little box, with some of your old clothing that has your sent on it. Make it a nice cozy spot for them. It will not only double as a nice place to sleep, but it will also make them feel secure.
http://aspcapro.org/sites/pro/files/blog/wp-content/uploads/2012/10/styrofoam.jpgThe other thing you can do, play with them. Get one of those fishing wands and just wiggle it about! Eventually, they all will start playing with it. Maybe momma will too since it sounds like she is extremely young.
Our Speck kitty was born outside to a very skittish momma, which is now pretty much an indoor kitty. I have to MAKE her go out to potty. She was nursing him on our porch one night, she ran when we pulled in, he got confused long enough for me to grab him up! I brought him in to say hi and handed him to my dad. He snuggled right up and went to sleep! LOL! Momma eventually had 3 more on my mom's bed! She is also not my dad's girl!
Then, the last two boys we got, the neighbors had moved away. Another momma cat came over with 2 of her kittens. The one was really playful, he's snoozing on my bed now! The other showed up a few days later and I grabbed him up cause he was shy. Brought him in, same thing! LOL! Of course, the momma kitty was so happy to get food and get them weaned. It turns out she had 6, all of which showed up here, but eventually went back to where she had left them. We kept the 2 she left with us!