You can claim the child as a Qualifying Relative, as Other (not as step-child). See screenshot below.
There are two types of
dependents, "Qualifying Children"(QC) and standard ("Qualifying
Relative"). Only a QC qualifies a taxpayer for the
Earned Income Credit
An unrelated person can
still be a Qualifying relative dependent, if
1. he lived with the taxpayer
ALL year and
2. His/her gross taxable income
for the year must be less than $4,050 (2016-17) and
3. The taxpayer must have
provided more than 1/2 his support
Read TurboTax Faq below for more information regarding dependents:
https://ttlc.intuit.com/replies/5187060
