For a fun and youthful finish, you can try two braids, which can be created in different ways, including pigtails for a cute and girly. A braids/pony combo look is the best of both worlds:
Kids hairstyles in a ponytail
Hairstyles for lil kids with weave braids ponytail
Natural hair ponytail hairstyles for kids
15 Photos Two Braids into One Braided Ponytail