There are a number of different sun shades you can use
Suction cups:
These are easily pulled down by kids.
They have limited lifespan.
They do not cover the window fully.
You can not open the window.
Roller Blinds:
These also have similar disadvantages like suction cup varieties.
Mostly suction cups used to attach it to the window.
Easily pulled down by kids
Towel:
We have also used this in the past and managed to break the window electric mechanism of our car. It is also not possible to see outside.