An Erie, Illinois school district has banned Todd Parr's The Family Tree due to a gay reference.

The colorful children's book is a New York Times bestseller and winner of the 2004 Oppenheim Toy Portfolio Gold Award. More than 2 million copies of the book have been sold.

The book's inclusion of the line, “Some families have two moms or two dads,” reportedly led to the book's exclusion.

Appearing on CNN, Parr said he was shocked to hear his 10-year-old old book was banned.

“I was disappointed,” he said of the decision.

“This book for me was just about how do you do a book for kids and depict every possible kind of family that you can in a picture book. And it just teaches about single parents and kids that are [of] different color, or divorce even. I just wanted a book that you could help as a springboard to introduce that there are all kinds of different families in the world and each one of them is special and important.”

Erie, Illinois School Superintendent Bradley Cox said via telephone that sexual orientation was not an “age appropriate topic for elementary school children.” (Watch the entire segment at CNN.)