It can be a really difficult situation if someone has claimed your child as a dependent for their tax return. In such a situation the IRS will not let you known who actually has claimed your child. In case you feel you are eligible and have all the required criteria with you to claim the dependent then you can file the return with the IRS. Once you file a right to claim you will need to be prepared for an audit. During the audit you will be asked questions and also asked for documentation based on the eligibility criteria. You will also need to provide them with school and medical records.