Stay at home moms have been fielding this one Forever. I love it when someone will chime in, "How can you stand to stay home? What do you DO all day?" (I love this one) Lemme see...
As others have said, it may be just a polite conversation starter of sorts. If it feels too nosy,it probably is so be creative. I seriously doubt anyone really wants to know what keeps a busy mom or dad busy all day.

As to the disability question, it is private business if you ask me. If I don't want to discuss anything about myself, I don't. Just because someone has poor to no manners with regards to asking personal questions, doesn't give them the right to an answer.

I love the creative answers others here have put forth. There are a million ways to answer unwanted questions. Pick one! My personal favorite: I Herd Cats. Yes! It does pay Really Well!
Ann Landers had two that I have used when necessary that I also love & are so simple & beautiful. They require being adept enough to change the subject but they are, as I said, favorites.

They are: "Why do you want to know?" & "I can't believe you asked that!"