I don't know for sure, not having read this book, but LGB #133, "The Rainy Day Play Book" was first published in 195l. The cover shows a little boy and girl playing inside a house (you're looking at them through a window; it's raining.) Illustrator is Corinne Malvern, whose realistic pictures of children were somewhat similar in style to Eloise Wilkin's. (My family had a large LGB collection during my childhood in the 1950's, and both artists were included. I didn't really differentiate between the two until I became an adult collector when I started my own family.) Could this be the book you recall? I haven't seen any other replies to your question yet, so I hope this helps. Good luck on your search!