You do not enter someone else's earned income from wages reported on a W-2 or their income from self-employment on your tax return except for your spouse's when filing as Married Filing Jointly. Your son can file his own tax return and on his return he Must indicate that he can be claimed as a dependent on someone else's return.
You should be able to claim him as a dependent on your tax return under the Qualifying Child rules provided he meets all the requirements. His income is not a factor under the rules.
To be a Qualifying Child -
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 the year, (b) under age 24 at the end of the year and a full-time student or (c) any age and permanently and totally disabled.
3. The child must have lived with you for more than half of the year. Temporary absences while away at college are considered living with you.
4. The child must not have provided more than half of his or her own support for the year.
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 must be a U.S. citizen or U.S., Canada or Mexico resident for some portion of the year.
7. The child must be younger than you unless disabled.
