It might be for balance despite the small size. On the human side, our pinky toes are important for balance despite appearing a little bit vestigial.
Another possibility/question I was idly wondering about is whether they were proportionately larger for juveniles and served some purpose that full-grown adults did not need. Maybe digging out of nests? - though I think specializations only for hatching (e.g. egg teeth) tend to disappear shortly after.