Not who you're replying to, but my take is that if everyone complied with their tax obligations correctly, nobody should have filed or owed taxes. The kid should probably have been a household employee. A household employee under the age of 18 is exempt from Social Security and Medicare taxes.

https://www.irs.gov/taxtopics/tc756

In addition, if they made less than their standard deduction, there would also be no income tax liability or filing requirement.

What probably happened was that the kid was incorrectly sent a 1099 form. This is wrong for two reasons. First, it's not needed for a personal residence or rental properties for investment, only for businesses. Second, a household employee is not a contractor, and should generally receive a W-2 (or nothing at all, in the kid's case).