Q. Can I claim my grandchildren if I have legal guardianship? Can I or not?
A. No. Having "legal guardianship" is not enough.
But, you haven't provided enough information to answer the question of whether you can claim them. You have to meet all the rules. Legal guardianship is not a rule. Being a close relative (i.e. grandparent) is a qualifying rule. But there's still more
There are two types of dependents, "Qualifying Children"(QC) and Other ("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, student status, a relationship test and residence test. Only a QC qualifies a taxpayer for the Earned Income Credit and the Child Tax Credit. They are interrelated but the rules are different for each.
The support test is different for each type. The support test, for a QC, is only that the child didn't provide more than half his own support. The support test for a Qualifying Relative is that the taxpayer provided more than half the relative's support.
See full dependent rules at: https://turbotax.intuit.com/tax-tools/tax-tips/Family/Rules-for-Claiming-a-Dependent-on-Your-Tax-Ret...
