AV-Comparatives provides certification for parental control software. Parental control solutions are tested against 2,000 URLs with undesirable content in different categories, and 200 child-safe URLs. In order to be certified, a product must block at least 98% of pornographic websites, have no more than a few false alarms on child-friendly websites, and have no severe unresolved bugs (or design flaws) discovered during the review.
The certification reports can be found here: https://www.av-comparatives.org/parental-control/