I'm all for kids working but punching almost half a regular working week on a 13 year old will seriously cut into their "let me be a kid" time. 

If they choose a payment plan, I recommend they pay it off in less than 90 days and the payments should be regular, every 14-30 days.

How do you overcome the objection from a landlord that a STR would create more problems for the owners than a regular rental would. i.e.- there would be more traffic and there is a permit to obtain from the County.  

If you're not bringing the financial piece of it, you can always promote other skills/services you have that can be beneficial to the partnership.

Albeit, the grass will require regular maintenance but it is a quick inexpensive fix.

So I want to see that they’re still getting paid this money, and the actual break down on the check stub of how much they get paid per hour, how much of it was overtime, whether they regularly earn overtime, any garnishments or involuntary deductions, year-to-date pay, etc.

There aren't really any mobile home parks close that I know of.But there is this neighborhood with 5000 sq ft lots that have MH and some older built regular homes.  

Do you find your experience using this strategy better than regular SFH 

Modular houses are not the same as a regular one.

Which means self employment tax.The residential treatment facility might be considered residential investment property or not depending on the level of care, regularity of assistance, and if the majority of tenants have long or short terms stays.A more careful analysis is needed for both of these situations to determine the taxable nature of these activities.