Moomin and the Wishing Star - Tove Jansson, Penguin Random House Children's UK

When Moomintroll finds a beautiful shiny pebble, Snorkmaiden thinks it might be a star - and if it is a star, then Moomin can make a wish! But wishes are difficult things to get right, and while Moomin worries about what his wish will be, the star's shine