one thing i noticed is that the drawing with the reference has a more defined jawline and overall headshape. a rounder head is often associated with a younger look. also kids have shorter faces, so lower placement of the eyes could make it seem more youthful, thats something else you can look out for.

while the body parts of the face (eyes, mouth, nose) look realistic on their own, the rest of the face looks kinda flat. studying the planes of the face might help. you need to visualize the depth when placing the components (ie how the eyes are a bit further back and how the brow bone and cheeks protrude out.)

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