If a child is entitled to Social Security benefits, such as after the death of a parent, the benefit is considered to be the child's regardless of who actually receives the payment.
Per IRS Publication 915 Social Security and Equivalent Railroad Retirement Benefits, on page 3:
Children's benefits. The rules in this publication apply to benefits received by children. See Who is taxed, later.
On page 5:
Who is taxed. Benefits are included in the taxable income (to the extent they are taxable) of the person who has the legal right to receive the benefits. For example, if you and your child receive benefits, but the check for your child is made out in your name, you must use only your part of the benefits to see whether any benefits are taxable to you. One-half of the part that belongs to your child must be added to your child's other income to see whether any of those benefits are taxable to your child.
Whether a child needs to file a tax return is based on their total income. Please refer to Table 2. Filing Requirements for Dependents on page 4 of IRS Publication 501 Dependents, Standard Deduction, and Filing Information to see if your child is required to file a tax return.
If you determine the child must file a return, a portion of the Social Security benefits MAY be taxable based on their other income levels. This is calculated on one of the Social Security Benefits Worksheets, which is automatically created after entering the benefits into the program. You can use the TaxAct program to enter their information to see if any of the benefits are considered taxable.
To enter or review information from Form SSA-1099 Social Security Benefits:
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.