My one daughter is now 3. I get complimented on her always using, please and thank you. I won’t take all the credit for that as I think some kids are easier to get to do certain things, but I always try and remind her if she forgets to be curtious, I also don’t respond when she’s whining at me. I tell her that she’s whining and she needs to ask nicely ‘please or thankyou’…so reinforcement of the behavior.
As for table manners, that’s out the window at this age…we’re happy if we can just get her to eat (she’s always been a terrible eater.) When visiting family they were appalled at me running after her with bites of food and that’s when I realized I catered to this bad table manners (or should I say, total lack of them), so we have implemented a new routine. I think it’s just asking them to do what you want and then following through with any consequences.
I have found that when it comes to behavior that you want to reinforce…books are the Best! You can find all sorts of books on manners. We have a book on an angel that visits when the little girl is naughty all day long, and I can’t tell you how much impact that had on our 3 year old. When she’s naughty we talk about the characters in the book and how it makes each feel…you can really see her thinking and trying to understand. I think it just gives some validation to what you are asking them to do.