If you set up a 401K plan with a big contribution for all employees, you can pay them a lot that's tax free for them (and you).
(But double-check that with a CPA just to be sure...)
Just because it's a little nuanced, let me say that if a sole proprietorship or a partnership where the two parents are the partners pays minor children, that income isn't subject to federal payroll taxes and usually isn't subject to federal income taxes either.
E.g., if a sole proprietor with two kids earns, say, $24,000 before paying the kids but then pays each kid $12K, the $12K isn't subject to federal income taxes because the $12K standard deduction shelters that income.
Further, if the two kids are minors, Social Security taxes, Medicare taxes and FUTA taxes don't apply.
One needs to check whether state or local payroll taxes or income taxes apply, but usually hiring minor children in a
sole proprietorship or a
husband and wife partnership is a killer tax saving gambit.
And two clarifications. One, you don't want to pay kids as 1099 contractors, you pay them as W-2 employees. Two, and as discussed in more detail in the blog post I earlier referenced, the job needs to be real.