It is not necessary to credit the reviewers of an online article, since they may not have contributed any content, but if you wish to do so, list them in the “Other contributors” slot.  If they did not play a role in reviewing the entire website, list their names in the middle optional-element slot after the title preceded by the label “reviewed by.” If there are more than two reviewers, list the first reviewer’s name followed by et al. If the date reviewed is provided, list it after the names of the reviewers:

“Vaccine Safety: Immune System and Health.” Reviewed by Paul A. Offit et al., 30 Mar. 2018. Children’s Hospital of Philadelphia, www.chop.edu/centers-programs/vaccine-education-center/vaccine-safety/immune-system-and-health.