Qualifying child requirements
Unless you and your spouse file a joint tax return, a child can only be a claimed as a dependent by one parent. This requires that the child not provide more than half of their own financial support and reside with you for more than half the tax year. This only applies to children under the age of 19, or under the age of 24 if attending school full time. Otherwise, they can't be your qualifying child, however, they might still be claimed as a dependent if they meet the test as a qualifying relative. If your child is away at school during the year, you can treat that time as if the child lives with you. In addition, you must also ensure that you are not an eligible dependent for another taxpayer. Taxpayers who qualify as dependents to someone else are ineligible to claim their own dependents.