Benefits for Social Security survivor children’s benefits are generally made out to a parent or guardian. They are taxable income, but most children do not have enough income to owe taxes on the benefits.
According to a recent article “Are Social Security survivor benefits for children considered taxable income?” from Investopedia, the only way the benefits would be taxed if half of the child's benefits in a year, plus other income earned by the child in that year, reached the level that required a tax return to be filed and for taxes to be paid.
If half of the annual benefits plus the child's other income is greater than a base amount set by the IRS, then a portion of the benefits is taxable.