don't confuse INCOME tax with SELF-EMPLOYMENT tax.. They are separate and different. Your child's INCOME is less than $12,550 so there is no INCOME tax, but there is a SELF-EMPLOYMENT tax.
I do not see where the IRS language states IF THERE IS ANY FILING REQUIREMENT - where is that reference?
from the IRS website:
https://www.irs.gov/instructions/i8962
Household income.
For purposes of the PTC, household income is the modified adjusted gross income (modified AGI) of you and your spouse (if filing a joint return) (see Line 2a, later) plus the modified AGI of each individual whom you claim as a dependent and who is required to file an income tax return because his or her income meets the income tax return filing threshold (see Line 2b, later). Household income does not include the modified AGI of those individuals whom you claim as dependents and who are filing a 2021 return only to claim a refund of withheld income tax or estimated tax.
