No. A non relative must live with you all year to be a dependent.
No. A child, who is a dependent, must also be related to you, to be a "Qualifying Child" for EIC, the Child Tax credit, day care credit and Head of Household filing status.
You say you have "legal custody"? It depends on what that means. A "foster Child' is considered to be related. A foster child is a child placed in your home by a court order or government agency.
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 the taxpayer for the Earned Income Credit, the
Child Tax Credit. They are interrelated but the rules are different for each.
A QC only needs to live with you for more than half the year to be your QC dependent.
