This wallpaper totally reminds me of that room.
The speech bubbles make a nice pattern and I actually like it just as is, but hand-written messages are bound to happen in here.
These images from Custom Wallpaper Rollout make it seem like a teenager wrote on these walls but imagine using the wallpaper instead to document a child's early years. For example, as a toddler, a parent can write on the walls some of the funny and clever things the child says. Then as the child first learns to write his/her name, that would be recorded, too. More personal messages and drawings would be added in later years, too. It would be like turning your walls into a multi-year scrapbook!
Interested in other ways to personalize your wallpaper? Check out this post from last year.