You can figure out the duplicate child in the following ways:

Search for the child's name: Navigate to the child profile page. In the search bar, enter the name. 

Compare created dates or child IDs: Based on the child id/created date, you can find which child has created first.

Review profile details: Compare the information within each child's profile. Check for any inconsistencies or missing details which is a duplicates.

Analyze the child's ledger, schedule, and billing records: Check the child’s ledger, schedule, and billing information, delete the child which doesn’t have all this information.