I saw a picture (probably on pinterest?) that had both the walls and sloped ceilings wallpapered, and it looked amazing. My other suggestion would be to agree - maybe just the window wall.

Love the wallpaper, and congrats!

I think just doing the window wall would work well. If you wallpaper the pitch too it may make the space feel too closed in.

If you do the ceiling leave the window wall solid, or just do the window wall.

I like the pattern of the wallpaper but really dislike gray for a childs room Kids respond to color as for where to put the wallpaperI would do the window wall to give you what you love and not create a huge amoount of work removing wallpaper in a couple of years when he has a favorite color that will change yearly.

Voting with just the window wall. It’s going to totally overwhelm the room if it’s on too many walls.
I also agree that grey may not be the best choice once your child is older.

I’d do the window wall and paint other walls the cream of the wallpaper. It seems like a nice neutral background for all the colors that will come and go over childhood. For instance, it would be smashing with touches of red.

i love the paper and i think your room is taller than it appears in a photo, based on the window. i almost think it will be the trash compactor from the first star wars movie, rather than the ceiling falling... squished in from both sides. i'd go with the window wall.

I think your particular wallpaper selection is the worst match for this room's geometry. If you look at examples of wallpapered rooms with sloped ceiling, they mostly use wallpaper with repeating patterns and very small offset, making it easier to transition from surface to surface. I'm attaching a few examples below, and this article has many more.

Just imagine how many chopped up dolphins will you end up with if you try to wallpaper the window wall. Or the complex structure on the right. I can't believe it can look good.

The bottom wall will mostly be hidden by furniture, so no point putting it there. Since its this particular wallpaper you're attached to, I'd try treating it as a mural accent and cover the slopped wall on he left.

Window wall for sure. I think doing the entire room would be overwhelming.

I think you can wallpaper all but it might make the room close in. Just lower walls and back wall might be a good choice. Though I like your choice of wallpaper, you might want to think about distinct black and white .... as *they may* provide the most stimulus to a child's brain development. Here's an interesting article.... nonetheless, my child seems to have turned out fine without black and white wallpaper :)

"Researchers have repeatedly shown that newborns prefer to look at black and white geometric shapes, rather than bright colors or pastels." http://huggamind.com/highcontrast.php

I’ve seen rooms with all the walls and ceiling papered and they looked spectacular. And I absolutely love the paper you’ve chosen. You can add color and pattern with textiles and objects. Books, for example add great color in a nursery. If your paper was circus characters, it might be too much but this paper would be like sleeping in a cloud. Have fun with it!

Moby Dick should go on the lower side walls. I wouldn't want whales on the ceiling - just not a natural location.