You have three years from the filing deadline to file an amended return. You may claim them if they lived with you for more than half the year.
A child closely related to a taxpayer can be a “Qualifying Child (QC)”
dependent, regardless of the
child's income, if:
1.
He is under age 19, or under 24 if a full time
student for at least 5 months of the year, or
is totally & permanently disabled
2.
He did not provide more than 1/2 his own
support
3.
He lived with the relative (including temporary
absences) for more than half the year. See below if they didn't live with you
4.
He is younger than the relative (not applicable
for a disabled child)
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 (this
essentially means that you have the parent’s permission to claim the child, if the child also lived with the parent more than
half the year)
6.
If the parents of a
child can claim the child as a qualifying child but no parent so claims the
child, no one else can claim the child as a qualifying child unless that
person's adjusted gross income (AGI) is higher than the highest AGI of any of
the child's parents who can claim the child.
https://turbotax.intuit.com/tax-tools/tax-tips/Family/Rules-for-Claiming-a-Dependent-on-Your-Tax-Ret...
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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 a relationship and a residency test.
A person can still be a Qualifying
relative dependent, if not a Qualifying Child, if he meets the 6 tests for
claiming a dependent:
1. Closely Related (nieces and nephews count) OR live
with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4,050 (2016)
3. The taxpayer must have
provided more than 1/2 his support. (note how this is different from the QC support test)
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. This means that the parents are allowed to let you claim the children, if the children live with you. If they don't live with you , you may only claim the children if the parents do not have enough income to have to file a tax return..
