The Deep Book 1 & 2
If you have children who watch The Deep on Netflix or CBBC, then these books are a gas. I illustrated two over the summer and have a number of others in the pipeline. The stories are terrific fun (despite the dodgy illustrations by some old bloke) and really well pitched at younger readers and parents wanting to read longer novels with their kids. They still a touch grown up for my 5 year old, so I'm going to say 6+ is a good guide.