As a child in the mid 80’s I read a book with a blue cover that only had the title (I am pretty sure it was the book cover as well), because I was trying not to judge a book by its cover. The book was science fiction about some children who were being replaced by clones of themselves so they could ditch school, and eat candy, and play- a little similar to a Pinocchio Treasure Island story. Until one day the children had stomach aches from eating too much, and not getting exercise, etc. and wanted to “go home”. I remember something about the rain melting the “aliens” or clones like cotton candy. I can’t remember much else and at first thought that maybe it was a Ray Bradbury book? At any rate I have been trying to find the title and would love if you could offer assistance.
This might be Mildred Ames’s Is There Life on a Plastic Planet? The ditching school and eating junk track but the rain melting does not.
I hate to post a spoiler, but there is a Ray Bradbury short story called “Rain Rain Go Away” that ends with the characters melting in the rain, although the rest of the plot is different from your memory. You might be mixing up two different stories.
I was coming over to mention Is There Life on a Plastic Planet…but I see someone beat me to it!