A Matter of Time
When you're 2, success doesn't necessarily breed success but it does breed willingness to keep trying. If you expect your child to say "please" at all the right moments when he's just learned to say the word, you'll be setting him up to fail. The more he fails, the more discouraged he'll get, and the less interested he'll be in learning. So be patient and offer lots of encouragement.
Nothing your little one learns is more important than speech. The more you talk to her, the more she'll understand things and talk herself. But don't expect her to use words the way you do. Your toddler may be able to say "promise," but that doesn't mean she's likely to leave the park without a fuss. At 2, "I promise" is not a moral commitment but a formula that she's discovered buys her time. And she often needs to buy time because while you complain that she's always dawdling, she can't understand why you're always in a rush.