Is it ok for my story to be just an adventure and show off all the things my character does at preschool without having him really grow in the story or have a moral at the end of the story? and just have the readers join him on one of his days at preschool?
Books for the preschool set don't have quite the same sets of rules as those for older children or adults. Plots are usually pretty light, so you are probably fine. It would, though probably be easy enough to show the character being worried at the beginning and happy at the end.
It wouldn't have to be an over complicated plot or anything. Something as simple as what chicagoliz mentioned would be really easy to incorporate into the story.
i have finished my book you can get it if your interested by going here http://www.blurb.com/b/5527641-ty-s-preschool-adventure