I am working on a provisional patent application for a household object. The invention is a simple item that comes in a large and small size. Do I need to file separate applications for each size, if they-are otherwise similar in look and function? I have the techical drawings for both.
The invention is a simple item that comes in a large and small size.
Wrong. Unless you're dead-set on shooting yourself in the foot, the invention can be made in any of a continuous range of sizes. If you plan to manufacture two sizes, that's fine. But I'm guessing your invention could be made to be any size between these, and even somewhat larger than your large size and even somewhat smaller than your small size. The point is the invention is more general and sweeping than the specific examples you're planning to manufacture, and your patent should try to reflect that as much as possible to get a reasonable scope of protection.
Do I need to file separate applications for each size, if they-are otherwise similar in look and function?
You can always file a single application to start with. If the PTO decides multiple applications are needed, then they impose a so-called "restriction requirement", and you have the opportunity at that time to file the multiple applications that are needed. It sounds like this would be unlikely to happen in your case (but keep in mind I don't know the details of your case, and, besides, I'm not a patent attorney either).