Why kids repeat the same phrase three times ?

Hi, I'm Dora.

I usually think questions are hanging all around our world.
This article is surely one of them.

Why kids used to say the same thing three times, whether
American kids or Japanese kids, especially when they are
upset or so much delighted ?

For example :

One day I was shopping in a huge mall that is in a Chicago suburb.
There was a family whose daughter was about the age of nursery
schools. She had blond and curly hair and pretty face so that
she was like a beautiful doll.

I assumed that she was asking a some kind of favor to her
parents, like as having an ice cream or buying something.

Then she said, in almost singing voice.
"♪Right now, right now, right now♪"

The next example is in a movie which is the one of the greatest
title of Meg Ryan and Tom Hanks, "Sleepless in Seattle",
its Japanese title is "めぐり逢えたら".

The kid in Seattle is arguing with his dad who is acted by
Tom Hanks, in their home.

Then kid says to his dad angrily and runs into his room.
"I hate you ! I hate you ! I hate you !!!!" Then bangs the door.

Why kids repeatedly say the same thing three times ?
Why not two times or more than four times ?

In my memory of my kid's period, we used to say something three
times, like as "バカ！バカ！バカ！" or "イヤ！イヤ！イヤ！" or
"汚ぁ〜い！汚ぁ〜い！ホント汚い〜！".

What do you think about that ?
Do your kids say something in those way ?