TOP THREE TITLES:

Piggy and Gerald Series by Mo Willems

The Pigeon Series by Mo Willems

Pete the Cat Series by James Dean and Eric Litwin

THESE TITLES RECEIVED AN EQUAL NUMBER OF VOTES:

Brown Bear, Brown Bear What Do You See by Bill Martin Jr. and Eric Carle

Click, Clack, Boo! by Doreen Cronin

DC Superhero Girls by Shea Fontana

Fancy Nancy Series by Jane O'Connor

Hildlafolk Graphic Novel Series by Luke Pearson

If You Give a Mouse a Cookie y Laura Numeroff and Felicia Bond

Llama Llama Red Pajama by Anna Dewdney

PJ Masks by various authors

Splat the Cat by Rob Scotten

Team Umi Zoomi Series by various authors

The Day You Began by Jacqueline Woodson and Rafael López
The Giving Tree by Shel Silverstein
The Kissing Hand by Audrey Penn and Ruth E. Harper

The Legend of Rock Paper Scissors by Drew Daywalt 
Uh Oh! Gotta Go! Potty Tales from Toddlers by Bob McGrath