In children's literature, a series refers to a collection of books that share common characters, settings, or themes, often released in a sequential format. These books may feature the same protagonists facing different adventures with each installment or delve deeper into a particular universe or concept. Series can encourage kids to develop a reading habit, as the continuity of characters and plots can keep them engaged and eager for the next book. Popular examples include the "Magic Tree House" and "Percy Jackson" series.