Robert Gilmore has written several entertaining and informative children's books on quantum physics (Alice in Quantumland, The Wizard of Quarks, Scrooge's Cryptic Carol). Facts and Mysteries in Particle Physics may be a good one for Dad if he doesn't have a solid background in physics (or your little one--not too heavy on math prerecs)... I personally liked the Gilmore series as a youngster. There is a lot of humor, and he weaves in other topics in physics that relate to quantum mechanics and particle physics...
