WebMD's Teeth Anatomy Page provides a detailed diagram and A normal adult mouth has 32 teeth, which (except for wisdom teeth) have.
In all, children have 20 baby teeth - 10 on the top and 10 on the bottom. These teeth act as placeholders for the adult teeth that grow in after the baby teeth fall.
We get baby teeth because as a child, our mouths aren't big enough for a full set of adult teeth, but kids still need teeth to chew. So all people.
Children's teeth begin developing in the fetus. Good nutrition from the Illustration demonstrating the age of eruption of adult teeth. Click Image to Enlarge.