There are two types of dependents, "Qualifying Children"(QC) and
standard ("Qualifying Relative" in IRS parlance even though they
don't have to actually be related). There is no income limit for a QC but there
is an age limit, a relationship test and a residence
test. Only a QC qualifies a taxpayer for the Earned
Income Credit and the Child Tax Credit.
The child may qualify as his dependent, but because they are not related, your child cannot be his qualifying child for the child tax credit, earned income credit or Head of Household filing status.
A person can still be an standard dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:
1. Closely Related OR live with you ALL year
2. His/her gross taxable income for the year must be less than $4150
3. You must have provided more than 1/2 his support
Whether a qualifying child or qualifying relative:
4. He must be a US citizen or resident of the US, Canada or Mexico
5. He must not file a joint return with his spouse
6. He must not be the qualifying child of another taxpayer**
He must have a US social security number or tax identification number (TIN)
**In addition to the above requirements, to claim your boy/girlfriend's children, they must meet all of the above requirements and:
--- your boy/girlfriend must not be required to file a return,
--- he/she does not file a return claiming the children
