Jax has the most adorable way of saying "Yeah!" for everything. The opposite of "Yeah" is "Nope." We have taught him "Yeah" by accident, because we say it all the time, and rarely say "Yes." We have taught him "Nope" on purpose, because it's so much easier and cuter somehow to have your toddler say "Nope" to you instead of the harsher, "No."
He has said, "Thank you" really well for quite some time now. He says it with a cheerful tone of voice, and says it very frequently. Probably because I use it all the time too - especially to reinforce his positive behaviors. He rarely says, "Please", probably also because I forget to use it all the time.
I haven't forced the issue (for example, insisting he say "please" before I comply with his request or giving something to him). This is partly because I am also really forgetful about saying "please", and partly because I consider tone of voice to be of much greater importance in polite communication than saying certain words. I've heard plenty of ugly-sounding "please will you's" and plenty of very cheerful and polite-sounding "will you" without the "please." So I work with him on having a cheerful tone of voice when he asks for something, more than I work on "please."
If he asks for something in a whiny or frustrated tone of voice, I just repeat his request back to him with a very cheery tone of voice, modeling the way I would like him to ask. He them immediately changes his whiny/frustrated tone/behavior, and responds with an excited little, "Yeah!"
Lately, I sometimes will also be more specific than just modeling, and let him know that he doesn't need to cry / yell / whine, that he needs to ask me nicely. Sometimes I don't correct the poor behavior, and just say, "Jax, can you try that again? Please ask Mommy nicely!" And he will change his tone promptly.
To work on both the "thank you" and "please" issue a bit more however, I decided to get cute books we found at the library. One where a little bear says "thank you", and one where a penguin learns to say "please." The trouble with behavior books is they often have the character exhibiting such poor behavior for a large portion of the book, and finally learning their lesson on the last few pages.
I like the Bear Says Thank You book, because Little Bear already knows how to say thank you. He asks his Mama Bear for various art supplies, and when she provides them (Here you go, Little Bear), he says a huge "Thank you!" with a page all to itself. At the end, he uses his art supplies to make a poster that says, "I Love You" and gives it to his mommy. The only thing I change in the words, is I add "please" to the end of his requests. It is absent from the book because they are working on one thing at a time, but it's easy enough to add it in when reading the book.
Penguin says Please is good too, but it does have the penguin begging for things in an insistent manner, "Give me something to eat! Give me something to drink!" I really don't care for the phrase "give me" AT ALL, so I substitute, "I need." Then when the mama penguin corrects him, she says, "No, no Penguin, you must say please", which I change to "Hmm Penguin, first you must learn to say please." I try to use "no" for strong correction, and not for gentle teaching moments, and I want mama Penguin to do the same. He quickly listens to her, and rewords all his requests using "please." She responds with "Very good, Penguin". At the end of the book, he forgets to say please again, and says, "I need the other sock!" When you flip the page, he says, "Please!" Even the first time I read it, Jax giggled at that last request of the penguin, because he was able to understand the penguin was supposed to say please, and he didn't even after learning his lesson. It was a bit humorous the way the book was laid out, and he got the joke. He still giggles at that part every time we read it.
The Penguin book has helped us a bit in the "please" department, and the following incident occurred a few days ago.
Jax was sitting at the table eating a snack. I was cleaning the kitchen.
In the silence, I heard his little voice say thoughtfully, "Say please, not yeah."
I giggled, then thought, Who taught him that?". After asking everyone in the house, we concluded no one taught him that; he thought of it himself.