Which Way Round the Galaxy — Cressida Cowell

In this action-packed fantasy adventure, from the internationally bestselling author of How to Train Your Dragon, a lost Magical Creature turns up on Earth, leading four siblings to journey off to a forbidden planet of fire and ice to save him.

There is no Magic here on Earth. At least, that's what you've been told. But in an ordinary-looking house in an ordinary-looking village live a group of children who have just uncovered a secret.

A tiny and helpless Magical Creature named Bug, lost far from home, leads the O'Hero-Smith children on another Star-crossing adventure across the galaxy. K2, Theo, Izzabird, and Mabel have a secret plan to get little Bug back to the fiery ice planet where it belongs, while proving to their parents that they can be trusted with Magic along the way…
 
But a witch's curse, venomous snowsnakes, and a gang of fighter robots are waiting for them through the Which Ways. The fate of the galaxy is once again in their hands -- they better not mess it up!