First, click on a house, then "upgrade". It'll cost you 55 wood and stone (and more each time you upgrade), but it will also allow you to have another peasant.
Now, click on a woman peasant, then "Get a child". Congratulations, a baby is born! He or she will be able to work at his/her 14th birthday.
If you don't want an empty village, you have to feed your peasants and avoid curses.
In order to do this, send a man to the job of "Farmer", you must click him and then click "Farmer". Then, click a woman and click "Prayer", she will get Gods' Points and avoid curses. Send your last man on Lumberjacking or Stone Farmer to get more peasants by upgrading your houses when you have enough stock. Then, get another child, get resources, upgrade your buildings, then yor houses...
Okay, this sounds boring, I know... that's why I've added something else in the game : You must know... your village can't last alone... to avoid this, you must make blood flow and take over territories... show you're the best Celtic Player!
Now if you want to know what I'm talking about, register here and play!