If you have multiple children that you would like to add to the same group, they can be added the same way as other group members.
Admin adds the child as the member to the group and you as the guardian. You will then receive a group invite either via SMS or Email or in the app if you already use the app. If you have multiple children, you will get an invite for each of the children.
or
Admin shares a group code/link with you that you can enter in the Spond app. If you have multiple children in the same group you need to add the code and follow the steps for the first child, then do the same for the next.
When both children have been accepted in the group and they are invited to events you will be able to respond on behalf of both separately. If you are invited as a guardian, you will also be able to respond on behalf of yourself.
Relevant articles:
What does the group invite look like and how do I accept?
How to I get access to a group with a group code?
How does the app work for me as a guardian?
How can I add another guardian to my child?