How do I tame a stray kitty?

We have had a stray cat around here for a while and noticed she was pregnant. A while ago we noticed that she wasnt fat anymore we knew she had her kittens. My dad told me I could get a kitty but he told me just to try to tame this one instead. I actually held it for a little bit but now every time I try it runs away. And it runs under the house. There is a hole in our siding that I cant get to to cover it up and every time i try to get close to it it runs under the house. I really want another kity, (I have had a few before and did really good with them, they died of old age.) What do I do to tame it?