If client request the other parent's return from IRS, probably is going to take 2-6 months. If it is feasible or correct, I would rather use the guardian's tax rate to report the child's tax base on the quarrian's rate.

Form 8915  line A is for parent's name. If I put guardian's name  and SSN#. would that cause for red flag?

How do you calculate the child's unearned income? she did not work. Do I report all her 1099-R box 2 taxable amount plus taxable social security income as unearned income.