I have 3 children over seas,we have been supporting them fully for the last 3 years.How do we claim them on our taxes?Or is it even possible?We have been fighting to get them here for the last 2 years,with no luck so far.

Requirement of dependents:
You cannot claim a person as a dependent unless that person is a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico, for some part of the year.

Where is your spouse located?

Is he/she with the children?