We start from day 1. We model it when they are too little to speak. Rolling a ball with your 6 month old "thank you for the ball" "can I please have the ball?" Once they begin to speak and "ask" for something (maybe at that point it's more of a point, reach or mumble) we tell them what they are supposed to say "Mommy can I please have some milk?" Hand them the milk and say "Thank you Mommy". Of course a 12 month old can't say the full sentence but it's ingraining in their brain.
I had a 45 min stand off with my daughter when she was 14 months old. She knew the word "please" but refused to say it when she asked for milk. She repeated every other word I asked her to say but when I said "please" she looked me dead in the eye and refused to say it. I held my ground and she eventually caved. We never had that discussion again.
Manners are paramount in my home and I do not tolerate rude children. Because it's just what they've always known, we've never had any huge manner issues when out in the world. Of course, they are kids and they slip but they are always reminded. We were recently at a birthday party and of the first 5-10 kids to get cake, my son was the only one to say "please" and "thank you" to the parent serving it. We hosted a holiday party on Saturday and I had a few kids ask me for something with no manners at all. I reminded them to say their pleases and thank yous. I just don't think there is any excuse for kids to not be doing that.
We start from day one as well. I like to say it and sign it so before they start speaking they can sign it to me. When they begin speaking I encourage them to speak the word as they sign it so they being learning how to try to say it as well. :-) Both my kiddos were early talkers and could say things like, "May I please have milk," by a year however they still loved to use the signs. It helped a lot when they went through the shy stage with other people. They may have felt too shy to use their words but they would still sign "please" and "thank you." We also say please and thank you to them as well so that they know even grownups need to use their manners. :-)
From birth! They learn from example and my kids have showed manners since they could talk. My son used to say "de-do" as thank you when he first started talking. You'd be amazed at what they pick up on if you are consistant with doing it yourself!
Its started from when they are born. We use it daily for everything in our home. We teach by example in our home. I've also had a battle with my ydd, as Luv did with her lo. Mine doesn't get what she wants unless she asks, and uses her manners. Right now she is 3 and is in her demanding stage. She thinks that if she just demands things she will get them. When she doesn't, she gets mad. She gets 1 warning that if she doesn't stop she gets time out for the temper tantrum and she is told that she knows she will be ignored when she makes demands. She can ask for whatever and I will answer her, but I ignore demands.
start now when they understand the concept and can say a bunch of stuff now that my 3 yr old is verbal, we make her say please and thank you when she asks for stuff or thank you when she receives stuff
When they start talking...I say thank you when he gives me something or vice versa. I say bless you, excuse me, thank you you're welcome and suddenly you will hear "kaku" (thank you )my two yr old knew such phrases before shapes and colors were formally introduced