In the "FREE/BARGAIN - Children's, YA - 2015" thread gabby98
pointed out that several Dr. Seuss ebook apps were on sale at iTunes and Google Play. I checked and Amazon also has 5 on sale for $0.99 or 99 coins (3 of them earn 30 coins each). So, if you've got a bunch of coins just sitting around, this looks like a good use for some (405 for all 5) of them.
Green Eggs and Ham - $0.99/99 coins + earn 30 coins
The Cat in the Hat - $0.99/99 coins + earn 30 coins
Oh, the Places You'll Go! - $0.99/99 coins + earn 30 coins
One Fish Two Fish Red Fish Blue Fish - $0.99/99 coins
Dr. Seuss's ABC - $0.99/99 coins