The first stage of exfoliation usually begins near the 6th birthday, depending upon the time in which the baby teeth erupted.
A complete set of baby teeth has typically erupted when the child is 3 years old. Once fully erupted, a child has 20 primary teeth which will exfoliate or "fall out" and be replaced by permanent or "adult" teeth.
The second stage of eruption/exfoliation occurs near the 7 1/2 to 8 years of age. Some dentists refer to this condition as the "ugly duckling stage." This is only a transitional stage. Under normal circumstances, as the jaw matures and grows and the canines erupt, the incisors will straighten up and the gap will be closed. Meanwhile, no braces are needed.
And, the final stage occurs when the primary molars exfoliate at approximately age 11-12 years old. Remember that because all children are different, the exact age for tooth exfoliation will vary.
Here is a closer look at the exfolation schedule: