Based on the age of your oldest child, he isn't eligible for the $2,000 tax credit, but may be eligible for the $500 credit. If he lived with you for more than half the year and you financially supported him (you must provide more than 50% of his support) he is a qualifying child for purposes of the $500 Credit for Other Dependents.
You can read more about it here: What is the $500 Credit for Other Dependents
