Oh, I have a suggestion for a book you might like to share with your little boy, alongside whichever everybody-loves-preschool book he'll have seen already. It might reassure him that it's OK if he dislikes preschool, despite all the messages to the contrary that he'll be getting from everybody else.
I've copied the following from a post I made a few years age.
When I'm at the library I always pick up those books about starting school or nursery and leaf through them. I know exactly what will happen: child, possibly reluctant at first, goes off to school or nursery, decides it's a fun place, story over. I can't help myself. I have to read them anyway. I guess I am hoping against hope to find one that will have a different ending, which acknowledges that not all children enjoy school.
WELL, IT EXISTS, AND I FOUND IT! Rosemary Wells' "Edward's First Day at School."
After a week of unhappiness at preschool, here's the text of the last few pages:
"On Friday, Edward's teacher said, 'Not everyone is ready for the same things at the same time.'
"'Well, we'll just take him home until he IS ready,' said Edward's mum and dad.
"'Be ready soon!' shouted everybody. 'I'm ready right now,' said Edward.
"'What are you ready for?' asked Edward's dad. 'I'm ready for my sandwich,' said Edward.
"'And Bunny is ready for his bug soup!'"
There are two other books in this series, with similar plots.
Check out the review it received from the School Library Journal: "Edward is not a helpful role model for young children... Wells's characteristically droll, cuddly creations do not rescue the series from its exceedingly counterproductive
message. Buy another copy of Watty Piper's classic The Little Engine That Could (Putnam, 1978) to help children bolster their confidence."
("Buy another copy"? So if the first copy doesn't get the message across, let's keep piling more on until the child collapses under the weight of all that Positive Mental Attitude...)