He can claim his child if the child lived with him for more than half the year (or half the time since being born in case of newborns).
He can claim you, if you lived with him all year.
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. His biological child, that lived with him is his QC.
In your case, a person can still be a standard dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a
dependent:
1. Closely Related OR live
with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4,050 (2016-17)
3. The taxpayer must have
provided more than 1/2 his support
In either case:
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 or be claiming a dependent of his own
6. He must not be the
qualifying child of another taxpayer
