The kiddie wallpaper is also interesting... and consistent with the childhood themes that seemed to have Brian's attention in the Pet Sounds/Smile era.
Curtain, not wallpaper. Here's Marilyn's explanation:
"He had a runner along the ceiling, like a curtain rod, and he wanted to close off the sandbox like a room. A lady from a yardage shop came to the house, and he picked out the material...the pattern he wanted was little children playing, so it would be like little babies playing in the sand. Toddlers sitting with their buckets. It was a drawing. The idea was that he would pull the curtains closed, and it would feel like you were at the beach."