Was your son under age 19 or a full-time student under age 24?
You are probably OK.
The requirement for a child under 19 (or full time student under 24) is that the *child* does not pay more the half of their *own* support. Who pays the support does not matter as long as the child does not. The child can earn any amount of money as long as it does not go to support.
---Tests To Be a Qualifying Child---
(Must pass ALL of these tests)
NOTE: If a child passes all of these tests he must say “yes” on his/her own tax return (if he/she files one) that another taxpayer CAN claim him/her as a dependent even if they DO NOT claim him/her)
1. The child must be your son, daughter, stepchild, foster child, brother, sister, half brother, half sister, stepbrother,stepsister, or a descendant of any of them.
2. The child must be (a) under age 19 at the end of 2018, (b) under age 24 at the end of 2019 and a full-time student* for any part of 5 months of 2019, or (c) any age if permanently and totally disabled and must be younger than you (or your spouse if filing jointly).
3. The child must have lived with you for more than half of the year (There are exceptions for temporary absences such as school, illness, business, vacation, military service).
4. The child must not have provided more than half of his or her own support for the year.
See Worksheet 3-1. Worksheet for Determining Support
5. If the child meets the rules to be a qualifying child of more than one person, you must be the person entitled to claim the child as a qualifying child.
6. The child is not filing a joint return.
7. The child must be a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico
*A full-time student is a student who is enrolled for the number of hours or courses the school considers to be full-time attendance during some part of each of any 5 calendar months of the year.
See IRS Publication 17 for more information.