The Family Plus Membership provides entry for:
You can add an Extra Caregiver for $30 which allows you to add a third named adult to your Family Plus Membership, so that a grandparent, nanny, babysitter, etc. may also use the membership and visit with your children. Please note – this option does not increase the total number of people who can visit at any time (two named adults of the same household, up to three children, two unnamed guests of any age).