What game are you referring to, and what device are you playing the game on?

If you are playing Virtual Families or Virtual Families 2: Our Dream House, then you can go to the Family Screen, click the "New Generation" button at the top, and your 4 year old will be grown up and ready to take over the house.

Alternately, you can let her stay in the house and grow up normally. As long as you purchase groceries for the house and place them in the kitchen (they are automatically added to the food supply) and you check on her often to cure any sicknesses she may get, she'll be fine.