When iis it possible for babies to mate?

by Lee
(Pleasant Hill, ca)

Hello guys

I found a rabbit in my front yard, very young. Two weeks later she had babies. They are 4 weeks old and so cute. When is it possible they might mate. I do have homes for three babies and I'm going to keep mom and a baby.

I hope someone can help Me!
Oh, the mother is a Lion Head bunny.