Playroom decor ideas?

[shalalala]

We've just moved into a house that has a playroom (approx 12ftx12ft). We've painted it a pale grey but i would love to jazz it up with some kind of design on the largest wall. Think mountains or clouds (wondered if clouds is a bit bedroom/nursery?). Any bright suggestions? Ideally something that can easily be removed as the kids grow up.

I used wall decals. You can get a huge range from various stockists. I think I found mine via etsy.

They come off with heat from a hairdryer (allegedly. Not tried yet).

We've got a map of the world that was made to fit the wall. I think it looks fab and will last until they're much older.