Since I am the mother to boys I see it as my duty to raise gentlemen. My two year old (well one week away from 3) is learning "Ladies First". But in our house it is "Ladies and Babies First" since I have to carry his little brother with me.
My 2 year old is very well versed in what he needs to call adults. I think it is too formal to call someone Mrs. So -and-So. Instead he will call a woman Ms. First Name and a man Mr. First Name. Many people are very impressed with his politeness and I simply reply... my job is to raise gentlemen.