Just before my son turned four, we decided to upgrade his room from a nursery to a "big boy room." This meant giving him a real bed(!) and adding some touches and accessories to elevate the space from a calming nursery to a room that really reflected his personality and interests. He LOVES animals so the first thing I did was to hang this jungle peel-and-stick wallpaper on the largest wall of his room. The wallpaper is adorable but what I love most about it is its neutral color scheme. Most of his room is blue, gray and cream, so this coordinated perfectly (and matched the paint color of his remaining walls, which is Benjamin Moore "Silver Chain."
We have a kid-friendly sofa in the room that we use for our nightly story time, and which he can eventually use for sleepovers (it pulls out into a twin-size bed!)
I also replaced the original dhurrie rug from his nursery with this plush braided wool rug, which is so, so soft. We spend a lot of time up here doing puzzles, playing, and reading and this rug makes it so much cozier.
One of my favorite ways to decorate a kid's room or playroom is to add acrylic wall shelves for books, artwork, and dolls. These shelves have always been in his room but we've since replaced the baby toys with big kid books that double as artwork for the wall. I regularly swap out the books based on season/holiday so we always have "new" ones to choose from.
I kept the remaining walls simple by adding a large hare print (no longer available, unfortunately), some fun accessories like a felt animal head and "Imagine" pennant, and DIY'd a Peter Pan quote to go over his bed.
One last project that we did together was to use our leftover wallpaper from the accent wall to wallpaper the inside of his closet, which is a fun little surprise every time you open the door.
Jacob loves his big boy room and we do too!