The first step (for any 401(x)) is to get a copy of the fee disclosure form 404(a)(5). More than you wanted to know:
https://www.dol.gov/sites/dolgov/fi...improve-transparency-of-fees-and-expenses.pdf This form will show your son what fees his account will be charged
in addition to mutual fund management fees. The right number is zero. I have seen numbers as high as 1.5% though I have not studied the subject enough to know that there are not higher numbers out there.
If the fee is outrageous, then your son should put enough in to get any match, then open his own IRA or Roth for the balance of his savings.