Don't the teachers in kindergartens teach them how?
If you are one of them, read aloud the words in the following picture and you'll know how:
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Saying sorry when you are supposed to doesn't makes you a loser, but if u don't, you are definitely one.
So, be courteous, say sorry to others when you have to. Mind your manners, together we'll make the world a better place to stay.
Peace =)