You may want to start with eggs for your son's breeding project, but I think your son may lose interest if he doesn't have something to show at the next show in your area. I recommend you find a reputable breeder, and get a couple of chickens that will be old enough to show this 4-H year. Quarantine, so you don't worry about your other birds. Let him pick whatever breed he wants for breeding stock, but be sure to choose a docile breed for a Showmanship bird. I suggest you choose a Bantam with a calm demeanor. My granddaughter has done well with Plymouth Rock Bantams that she bought from a breeder for $15. each. Many use game birds for showmanship because they are small and easy to handle. (Some breeds are skittish which makes them more difficult to show.) Have your son hold the bird frequently so it is very tame. He can teach it to stand on a table and to walk when touched under the tail with the side of a stick. He should know the steps to examine the bird, and learn about the breed so he can answer the judge's questions. Our fairs divide the kids into groups. Novice will be only kids that have not shown before, so the judge will ask questions accordingly. It's a wonderful experience for kids and great for building self-confidence. If you don't have a poultry leader in your 4-H club, I'm sure there will be one in a neighboring town/club that would be willing to help. You may get so interested you will want to be the leader! The 4-H office will guide you. Also, BYC is a great resource as you have already found out. The Standard of Perfection is very helpful and can be purchased used, online. Check out the links in the previous posts, and your son will do great. Good Luck! Let us know how he does.
CP