Well, as a TPA it's not my place, but whenever we are discussing wages to family members I tell them the pay has to be reasonable for the services rendered.
Now, as an employer who did this myself with 4 kids, one year I actually got a letter from the SSA questioning the wages to my youngest daughter based on her age. The kids did come into the office at least a couple of times a month to fold, stuff and mail billing statements and the occasional mass mailing (I'm old - snailmail BITD). I was paying them more than minimum wage, but not excessively so, at least not IMO. IIRC I kept them under the 1040 filing threshold.
Absent use of likeness, I'd not be comfortable with $24K for a 6 year old, that's for sure. I generally discourage letting really young kids into the plan, even if there are no NHCEs. One reason is the reasonableness issue, the other is I'm a big fan of having the parents gift the kids enough money every year for a Roth IRA contribution assuming the kids have earned income.