Hopefuly, your 4-H club will assign a Junior Leader for your son. This is an older 4-H member experienced with the project (in this case, a lamb) and able to teach younger members what they need to know. For the first year, I would expect this Jr. Leader to visit at least once a week with your son. This can be a phone call, or a meeting at the barn, leaning over the fence looking and talking about the animal. Expect this Jr. leader to work with your son to train the lamb, also.
In addition to all the tips already mentioned; make sure you attend ALL the meetings. There will be a wealth of information provided. Sometimes, there's so much that the younger members can't remember/understand all of it. It's less confusing if you or your husband attend with him so two of you are getting the needed information.
Good luck! 4-H is a wonderful organization.