Yea, possibly do a 'feature wall' in Downpipe and make it a backdrop for loads of posters and other colourful items. It is a children's area after all... :). If you don't mind, they can even use chalk to make their own art.

Maybe paint the rest in (brilliant) white.

Have you got enough to do half-walls - they look really cool (you could go to a dado rail height?) - great in that it won't show kid's finger/toy marks (include your skirting too), and you could do the upper walls in a lighter colour off-white of some sort (also take same colour over ceiling), perhaps Crown's Sail White which will be cheaper than F&B.

PS. top tip - get a cheaper dark undercoat for the first coat (maybe two) and then just use F&B for top coat and it will go further!!

What will the flooring be? Downpipe is also great for disguising a TV.

To take everyone's ideas a little further, what about mountain shapes. Big triangles of Down pipe mixed with various amounts of white to get different grey mountains all around the room?

That looks fab! How about laminate flooring, it’s relatively cheap and easy to clean. Or even cheaper get a nice big rug from somewhere like Dunelm with blue in it and place it over the current carpet, much less work too! What colours did you use on the walls?

How about cork flooring? It has come up to date now - soft and insulating.