Hi My Name Is Mack I Have Some Americana Chicks

Hi my name is Mack I have some Americana chicks about three weeks old one day they all appear healthy the next day one or more of them has no sense of balance and just lay down and die takes sometimes 1 or 2 days Can you tell me what to do to save them Some of my other chicken buddies said that they thought it might be new castle disease!!!!! Can you help me????