Not sure how it would work on a full room, but for a feature wall in a child’s room, this Ferm Living Owls wallpaper by Trine Anderson could be really effective.
Printed on WallSmart wallpaper (non-woven fleece), this non-woven paper is said to be easier and faster to hang – it’s one of those ‘paste the wall’ wallpapers. Slap on the paste, then hang the sections by ‘butting’ the edges together apparently.
It is £60 for a roll, with each roll around 10 metres.
Footnote: If you like that owl mobile in the image above, you can get that here too.