Loosened, teeth are expected in small children as primary teeth make way for the permanent set. When teeth move in an adult’s mouth, however, that's a sign of a severe gum disease. Teenagers can also experience loose teeth caused by gum disease, but it's less frequent compared to adults. Although small children expect to shed their baby teeth, loss of tooth as a result of decay , need for professional dental interventions.
From: http://www.pediatricdentists.blogspot.in/2012/02/why-do-teeth-become-loose.html#.Tz0jKU7-sDY.pingfm
