You do, however, have to have enough living space for a foster child. If you have a spare bedroom or if you have one child in a large room, you will probably qualify. If you live in a small apartment or condo and have several children in one bedroom, you probably will not qualify. Requirements vary from state to state so check with your local foster agency. They will help you determine how many foster children your home can accommodate.
Some people take one child while other take brother and sister groups.
Most agencies will license you for more children than you are planning on taking. If you and your family know that you want only one child at a time make sure your agency understands this. Foster agencies are looking for people who have a stable job and a steady income. You will have to provide documentation that you can support a child. The foster agency will just want proof that a child in your home will be fed and cared for.