My 1st grader is into anything sciencey at the moment so he is rereading all the Magic School Bus books. Beyond that rereading Captain Underpants, Frankie Pickle, Magic Pickle, Secrets of Droon seem to top the list.
My Kindergartener is into a bit more variety and loves series - She has read all the Ivy and Bean books, I believe all Judy Moody, most Dear Dumb Diary, and most Disney Fairies. She is currently reading the Nancy Drew and the Clue Crew books but has asked about the bigger Nancy Drew books.
I think I'm going to see if she wants to read the Bobbsey Twins books as we have a ton of them before we get into Nancy Drew. She is enjoying the Mrs. Piggle Wiggle books as well. There are a few easier series she reads (a few books a night if she has them) Arthur, Horrible Harry, Rainbow Magic.
Oh I forgot - she read and loved the Ramona Quimby books so I'd recommend trying those
