Ever since my kids were born, I wondered how they would perform in the hide and seek game. I now have a 2y and a 4y old. You can spot them both in the picture below.

And there are some things I noticed:
The 2y old does not get it (neither did the older one when she was 2), but learns fast by imitating his sister.
The 4y old starts to get it, but does not yet realise that her hiding place must be a secret. When she is hidden, she do is invisible for me (most of the time, not when she hides behind a tree). But she must always make some noice, like saying “I am here”.
And she understands the concept of the game: someone counts, the others hide, and then the searching starts.
Nevertheless, it is a great game to play regularly. Each time we play it, she learns a new hiding place, and she even find new ones.
Kids are so great!