Yes, that is correct. The website says only unvaccinated kids under 12 need a PCR test. "All unvaccinated guests ages 2 through 11 will be required to bring proof of a negative NAAT test (i.e. PCR) result administered by a verified third party within three days prior to embarkation date."
So a PCR test would be okay for a vaccinated under 12 according to the NCL website.