In order for an individual to be able to claim dependents, he or she must not be a dependent him/herself. Generally, an individual may not claim those who are married and file a joint return as dependents. In order to claim a child as a dependent, there are a few guidelines that must be met.
First the dependent must be your child (step, adopted, or foster), your sibling, or a descendant of the above (ex: nephew or grandchild). The potential dependent must reside in your home for greater than half of the year. The individual, at the end of the year, must be younger than 19, younger than 24 and a full time student for at least 5 months, or any age but permanently and totally disabled. If the potential dependent provided for more than half of his/her support for the year, than they will not qualify as a dependent.