I know, it sucks. Nobody wants to do it (unless they're REALLY in trouble. In which case, it's probably not enough anyway). I've noticed some real difficulties around this in day care lately. No one wants to say they're sorry, and nobody's happy.
I try to teach the kids how simple it is to make someone feel better. Really, one of the keys to working with children is hearing them and acknowledging their feelings. Tattling isn't a problem because it's really the tattler who wants attention. I just listen to how upset they are, and suddenly the reason they're tattling isn't so important (unless it's someone tackling a baby, of course).
So when you tell someone "I'm sorry," it means that you realize that they're upset, and you hear them. Most of the time that's all it takes. (Remind me I said that next time my husband and I are in a fight.)
One of the girls broke something of mine, I can't even remember what it was now (as all anger goes) but I was more hurt that she didn't say she was sorry for breaking it. And here we are a week later, and I'm still angry, when if she had said she was sorry it would've been instantly forgiven.
Anyway. If I can let go of my resentments against a four-year-old child for a moment, I can continue with my story.
After I noticed whatever it was she'd broken, she didn't volunteer a sorry as she normally would. I told her, "When someone is upset at something you did, it makes them feel a lot better if you tell them you're sorry."
She tossed a, "Sorry" over her shoulder as she kept on playing and I thought, you're missing the point.
I teach an early childhood behavior class and I always read a quote from "The Last Lecture," by Randy Pausch. I know it sounds schmaltzy but this is really something I use all the time (both in work and in my real life).
"Proper apologies have three parts:
1. What I did was wrong.
2. I feel badly that I hurt you.
3. How do I make this better?"
Usually by the time you get to #3, the problem is solved, because the hurt party can tell that you mean it. It's so ridiculously simple.
I try to emphasize to the parents in the class that saying "I'm sorry" to your children is just as important as expecting them to say it to you. It's not a one-way street. In fact, probably the best way to teach your kids how to say it is to model it yourself.
The ironic thing about "I'm sorry" is this: we don't want to say it, we'll hold back even if it hurts and the fight is raging on, but our stubborn human nature never wants to let us admit we're wrong. When it's SO easy to make someone feel better by hearing it.
At the risk of veering into starry-eyed hippie dippie territory... well, I'll just conclude that it would be a lot nicer if we heard more I'm sorrys.