When the group admin invites you to a group you will receive the group invite either via SMS or email. Click "respond to group invite" (If you are already using the Spond app you will receive the invite in the app as long as they have added you with the same details as you have registered with)
On the next screen you can add your first name and last name as well as if you would like to hide your contact information. If you are added as the guardian of a child you will see this role here. You do not add any information about your child here.