We're not a fan of reading the Mighty Machines books to my 4-year old, but maybe he'll enjoy reading them to himself when they're older. He was mildly entertained, we learned a little bit, but we won't read again anytime soon.
Bless this book for being a vox book and giving my pneumonia ridden voice a break, though you could make it a little simpler to start the audio for young ones.