If the grandchildren lived with you for the majority of the year without their parents, you may be able to claim them as dependents if the follows requirements are met:
From IRS Publication 501:
- Relationship - Dependent should be
- Your son, daughter, stepchild,
foster child, or a descendant (for example, your grandchild) of any of
them, or
- Your brother, sister, half brother,
half sister, stepbrother, stepsister, or a descendant (for example, your
niece or nephew) of any of them.
- Age - They must be under 19, or
between 19-24 and a full time college student?
- Residency - You lived with the children for the majority of the year (and the parents did not live with them for the majority of the year as well in your home).
- The child cannot be claimed as a
dependent if they provided more than half of their support.
- For older children, the cannot be
claimed as a dependent if they file a joint return.