Why is there only one form submission per person?

We have a club & some families have more than one child enrolled. We would like them to submit their registrations separately for each child. Can you please tell me how to make it so they can do more than one submission?

You can allow multiple submissions for the form by changing the Unique Submission option in your Form Settings to "No check".

Go to Settings > Form Settings > Show more options > Unique Submissions. 

Hope this clarifies your query.