Way back when, it must have been at some point in the summer, Naoko Takeuchi mentioned at Sailor Moon Channel that she and her husband were working on a picture book for kids.
The book came out last October and I finally ordered it off Amazon JP, having failed to find it in bookstores.
The book is titled, "Ooboomee and Chiboomee," which translated to "Big Boomee and Little Boomee," with boomee being pronounced "bow meh." The book was illustrated by Takeuchi's husband, manga artist Yoshihiro Togashi, while the text and design were prepared by her.