Shugo Chara!

Every child has an egg in their heart, unseen at first, an egg with the would-be self of their dreams. Hinamori Amu, part of a group called the Guardians, protect those eggs from becoming x-eggs, eggs filled with resentment and resignation that gives children troubles. Amu's job is to capture and restore x-eggs to their orginal form. She does this with the help of her three Shugo Chara (guardian characters or her would be selves), Ran, Miki and Su. Thanks to them she can change her character and abilities, and so fight against the mysterious organization Easter which aim is to find a special egg called Embryo using the x-eggs.

Synopsis from Anime News Network