Yes, a tuition "reduction" or "waiver" is totally tax free, if your children are your dependents and undergrad students. Technically, an actual "reimbursement" by an employer is limited to $5250 tax free. But, as long as the benefit is not reported on a tax document (W-2 or 1099-Misc) , it is considered a reduction, for college employees.
Graduate education is treated slightly differently. See page 8 of Publication 970. https://www.irs.gov/pub/irs-pdf/p970.pdf