Try the Mrs. Piggle Wiggle books. They are charming and funny in a very innocent, old fashioned way. I read them to my kids and some chapters made them collapse with laughter, especially a chapter in one called "The Fighter Quarrelitis Cure." (BTW, I was looking for level 4 AR to see what books are at that level and saw a whole list of Berenstain Bears books. Seriously? They also are delightful books but 4th grade?) Any, Mrs. Piggle Wiggle is around AR 5.