When your little one has a cough or sneeze coming up say "Catch that sneeze!" and pretend to sneeze in the crook of your arm. He'll hear you say "Catch that sneeze," he'll see you doing it, and he'll copy you. Make a game out of it and he'll have fun and will learn it fast. When our boy first started learning it I'd hug him and love him up when he did it right. Now that he's so proficient (grin) I just give him a nod of approval and praise him for doing a good catch. Of course, don't expect perfection. You get some inconsistency with a two year old, but you'll beam with pride when your two year old covers up a sneeze all by himself in front of company.