Whether or not you can claim your son for EIC and some other tax benefits depends on who was the custodial parent who the child lived with 183 nights or more in 2018. If you are that parent, you can claim those benefits while allowing your ex to claim the dependency and child tax credit or family credit.

Here is how it works:

For divorced or separated parents or parents who live apart, the custodial parent, if eligible, or other eligible person who the child lived with for more than half the year (183 nights in 2018), can claim head of household filing status, the credit for child and dependent care expenses, the exclusion for dependent care benefits, and the earned income credit. 

The non-custodial parent, if allowed by divorce decree or consent of the custodial parent on form 8332 or similar signed statement, can claim the dependency  and child tax credit. For post-2008 divorce decrees or agreements, form 8332 or similar signed statement is required. The child tax benefits cannot be split any other way.