What Causes Frequent Need To Urinate In Children?

My girl child 4 yrs age, she drinks more water frequently , urinate frequently.some times 2 times in a hour also while in sleeping she urinate her urine rutine examination result albumin nil sugar nil microscopic examination pus cells 2_4/hpf epi cells +/hpf rbc nil/hpc cast nil/hpf crystals nil bacteria nilothers nil