Is there a word to describe pretending things are alright to not scare children?

I want to say something much more meaningful than what is simply in the title (plus it's a bit long).

This might not be the best example but I find the main character in the movie "Life is Beautiful" exhibits whatever trait this is called perfectly.

Solution 1:

The idiom put on a brave face is appropriate:

to try to appear brave or calm

She tried to put on/up a brave face/front despite the pain of the injury.

It’s not specific to when you’re trying to protect a child from a harsh reality, but it’s often used in this context:

Why your kids know when you’re trying to put on a brave face

Solution 2:

You are probably looking for the expression :

white lie (noun [ C ])

a lie that is told in order to be polite or to stop someone from being upset by the truth.

(Cambridge Dictionary)