I believe they do have to file just like if they had a W-2. Just my opinion.

If you check out the filing instructions you will note that there are a couple of tiers.  One is total income earned and there is also that second tier dealing with self employment income.  Of course there is always the argument whether a 12 year old has a business just because someone decided not to pay them on a W-2 for the work they performed.

Try this:

Having Earned Income and/or nonearned income (investments) vs How they would file. These are different concepts.

If your person has to file based on the qualifications and regulations which apply, then the issue of how to file will arise. Kiddie tax, W-2, 1099-NEC, etc.