I have a 2½ year old, and this is his favourite book by far. He shouts for it EVERY night and will not go to sleep until it has been read to him. He also has the 'That's not my truck' from the series which he also loves. The books have 'Touchy-feely' pages, and the best thing about them is their bright and colourful pages, containing ALL the main colours in the spectrum, which are of course helping him to learn 'his colours'. The stories are great and easy for small children to follow and there is a white mouse on every page including the front and rear covers, which children love to search for. With the 'That's not my monster' book most of the pages refer to body parts such as nose, eyes, hands, ears and eye brows etc, this helps your child to learn the parts of his or her body. Also some of the monsters have four horns or ten spikes which helps to teach your child how to count.
These books are supposed to be suitable for reading level: ages 4-8, but I say buy this as a first book. As an 18 month old toddler will soon pick up the story and be reading along with you from memory, which is going to encourage your child to read.