Hello Sabrina. The only way to find out if the father has claimed them is to ask him - the IRS will not disclose private tax information such as this to members of the public. In general the custodial parent is the one who is entitled to claim the children as dependents (unless there is a court order that states otherwise). So if you are entitled to claim them as your dependents then by all means do so. If the father tries to claim them as well you may find that you can't e-file, as the IRS computer will recognize the conflict and refuse to accept the second of the two returns. If this happens then what you do is file a paper copy, claiming the children as appropriate. The IRS will investigate and resolve the issue, and interest charges and/or a penalty may be assessed against the parent who should not be claiming the children. So at the end of the day it does not matter whether the father (or anyone else) has tried to claim your children - if you are the custodial parent and entitled you will be able to claim them.