To allow members to edit addresses, etc, a group admin must first enable editing for this field by going to the group settings (the three dots in the menu) and to 'Member Fields'. Here the admin can go into each of the fields to choose who has permission to edit them; Only administrators or administrators, guardians and adult members or administrators, guardians, adult members and children.
When enabled, members can edit these fields in the app (not on the web) under Me (top left) > Group membership > select group and member and then edit the available field.
This feature allows members (and parents or guardians) to edit member information such as date of birth, address, custom member fields and add more guardians. It is not possible for guardians to add or change the children's contact information. It is admins who must add this to the member list.