The Word: Sorry!

Let's talk about the word SORRY!
It's an arbitrary word for a toddler to understand. The purpose of the word sorry is to convey remorse and understanding of your wrongdoing. Now, how does that translate to a toddler? Instead of forcing them to use the word sorry, squat down and firmly explain that they gave someone an ouchie. The consequence should not be seen as a punishment, rather an action, meaning "Ask them if they are ok? Do you need an ice pack?"
Does this often involve unnecessary usage of ice packs? Yes, but it helps get the point across to them. 
You also need to model this as a parent too! When they get hurt you say: Are you ok? Do you need an ice pack?