The current software has a feature that allows you to select your favorite thumbnails for each person. Those are specifically used for recognition purposes and should achieve the goal you are looking for! You can set as few as you'd like for each child.

 Managing favorite faces for a Person- this directly affects the Suggestions The number of favorite faces selected for each Person used for Suggestions is limited to a maximum of 100. Favorite faces are converted to face templates by the system. These are then used to find matches with unknown faces. Initially, TTP auto-selects 50 faces based on quality. By default, the initial list of thumbnails shown for a Person is sorted to show “Favorite faces” on top. You can change the sorting via the icon (circled in the screenshot below):...

Full details starting on Page 31 of User Guide. Available via the Help menu on the software.

Once you make changes, run the Regenerate Clusters and Suggestions from the bottom of the Settings screen.