Children need special care to protect their first "milk" teeth. There are several products which are designed specifically for children. Your dentist will be happy to answer any questions you have with regards to cleaning correctly and using the right products.
First or 'baby' teeth usually develop before your child is born and will start to come through at around 6 months. All 20 baby teeth should be visible by the age of 2, and the first permanent 'adult' molars (back teeth) will appear at about 6 years of age. The permanent 'adult' teeth will then replace the 'baby' teeth. It is usually the lower front teeth that are lost first, followed by the upper front teeth shortly after.
All permanent teeth should be in place by the age of 13, except the wisdom teeth. These may erupt any time between 18 and 25 years of age, although all children are different and develop at different rates.