The Mirror in Room Five Zero Five

Jack and Charlotte, aged ten and twelve, are on a vacation with their parents and their dog, Robbo. When they arrive at the Royal Hotel at Crinkly-by-the-Sea, they sense that something is amiss.
An old, lifelong guest of the hotel regales them with stories of children who have gone missing throughout the decades. They all had one thing in common: their families were staying in room 505 at the time of the disappearance.
Jack, Charlotte, and Robbo launch an investigation that leads them to the mysterious room, where they find a mirror that transports them to an otherworldly realm. There, they meet the missing children, who are alive and well-though they're periodically terrorized by a terrible monster.
The uncanny mysteries, unexpected turns, and unmatched courage make The Mirror in Room Five Zero Five a thrilling tale for young readers. It combines the wild imagination of C. S. Lewis, the adventurous spirit of Enid Blyton, and the humor of Roald Dahl. This dynamic adventure harks back to these authors' beloved tales but incorporates a modern slant that's sure to surprise and delight.