They can breed but there's nothing you can do to speed up the process, as they do it entirely by themselves. It takes quite awhile, and they only breed if the population is less than 1/3 of the number of houses IIRC. I could be wrong. And I do believe there's ways around it but I'm not sure on the specifics.
According to the Wiki, the number of villagers is around 1/3 of the number of doors. I say around, because it looked like the Wiki said that the villager A.I. doesn't stop breeding until the number of adults is at 1/3. So it's likely that there will still be children running around when the village hits the required number. Those children will eventually grow up, and put you at just over 1/3.
The way to get around it is to build a house in the village with long walls, and make every other block a door. With thirty doors, you'll get an additional 10 villagers. The Wiki said these are referred to as "Love Shacks".
I should also add, only doors with one side indoors count. And by indoors, I mean that there has to be a roof.
There are 10 types of people in the world. Those that know binary, and those that don't. Gamertag: Talon Omega