Why did Anna have to be shielded from all knowledge of magic?

The question is:

Why did they have to hide Elsa's power from everybody, why couldn't they tell about it to Anna ?

Well, their parents did not have any magical powers in the first hand. They did not have any knowledge about how to use that power and so they would not be able to guide Elsa about how to control it either. They hoped Elsa would learn it all by herself overlooking the fact that they are making her more insecure about herself.

Elsa loves Anna, but her power unleashes with the outburst of her emotions which can hurt others. She can neither control her emotions nor her power. Their parents could only think of separating the sisters until Elsa learns to control.

But what would happen if she found out before she did?

There are multiple possibilities in which the story could have unfolded. As much as I can imagine,

• The sisters would have a bumpy yet close relation. Both of them have suffered from loneliness, suppressing their feelings for each other, suppresing Elsa's power within herself and all.
• Elsa would have hurt Anna more physically in their childhood, obviously unintentionally.
• Anna could have suffered from trauma if the hurts were severe. And as Elsa loves her sister, seeing Anna suffering would take a toll on her mind too, only to release her power which can again hurt others.
• It would make Elsa more determined to control her feelings or emotions,which means she would have learnt controlling a lot earlier.