If your son lived with you for more than half the year, you should include him on your taxes even though you're not claiming him as a dependent.
By including him, you may get Head of Household filing status, the Child Tax Credit, and the Dependent and Child Care Credit if you would otherwise qualify.
When you enter the dependent, you say that he/she is "Your
child" (not you and your spouse if remarried),
He/she lived with you the whole year (or 7 months, etc)
“No” the child did not pay more than half of his/her own
support,
"Yes", you have a custody agreement, and
"Yes", the other parent is claiming this
year.
