You don't need any paper work to claim your grandchild as a dependent. For tax purposes, TurboTax will create any tax forms that are required.
In general, to be a taxpayer's qualifying child, the child must satisfy four tests, for each year, in order to claim them as a dependent:
Relationship — the taxpayer’s child or stepchild (whether by blood or
adoption), foster child, sibling or step-sibling, or a descendant of one of
Residence — has the same principal residence as the taxpayer for more than half the tax year. Exceptions apply, in certain cases, for children of divorced or separated parents, kidnapped children, temporary absences, and for children who were born or died during the year.
Age — must be under the age of 19 at the end of the tax year, or under the age of 24 if a full-time student for at least five months of the year, or be permanently and totally disabled at any time during the year.
Support — did not provide more than one-half of his/her own support for the year.