Gastronauts — James Foley

Sally Tinker, the world's foremost inventor under the age of 12, has an extraordinary new challenge. The brain-enhancing nanobots she is testing have been accidentally swallowed by her baby brother Joe. The only way to stop Joe turning into a superbaby and wreaking super havoc is to shrink herself and travel inside Joe's body on a journey to tackle the problem head-on. What could possibly go wrong?