Twenty year-old Kelsey Dangler and 21 year-old Christopher Perez, of North Platte were both arraigned on Tuesday.
Perez's attorney says he intends to plead not guilty.
Authorities say Dangler took her son, Zachary Simith, to Lexington Regional Health Center in February. She told police that Perez fell on the child while they were playing.
Medical personnel say the boy's injuries were not consistent with the account.