Users related data table – parent/child relationship

I am looking for a way to manage a table of children, that will be related to a website User (parent). Please see example below and recommend any plugin or other method that may help deliver such functionality.

Example:
I am building a camp website where administrator will be able to have an list of children to import (name, age, counselor, etc). Then invited Parents will be asked to signup for the website that will have calendar, events, rsvp and volunteer sign-up features. I’d like for there to be a many-to-many relationship between the Users (parents) table and the related child table.

Thanks in advance for any help.