This is is a Japanese-language book or magazine devoted to fashion or cosplay ("COStume PLAY"), and may contain actual sewing patterns for creating your own clothing/costumes, as well as photos of completed outfits.
You'll want to go outside and play like crazy after flipping through this delightful softcover book! It's filled with page after page of color photos of gorgeous dolls in many media by different artists, depicting kids enjoying their downtime. Riding bikes, playing cat's cradle, spinning tops, dressing up--these and tons of other childhood pastimes are shown. Hey, d'you wanna come out and play? Text is in Japanese.