The first baby teeth come into the mouth are the two bottom front teeth. You will notice this when your baby is about 6-8 mounths old. Next to follow will be the 4 upper front teeth and the remainder of your baby's teeth will appear periodically. They will usually appear in pairs along the sides of the jaw until the child is about 2 1/2 years old.
At around 2 1/2 years old your child should have all 20 teeth. Between the ages of 5 and 6 the first permanent teeth will begin to erupt. Some of the permanent teeth replace baby teeth and some don't. Don't worry if some teeth are a few months early or late as all children are different.