What trim size should I use for my children’s book? That’s another question that comes up. OK, and just like trade books, the children’s book have standard sizes also. I mean you just have to really walk into the bookstore and take a look and you’ll see. Alright, you don’t want to…you want to stick with the standards. I mean there’s basically three different ones. There’s basically a square size which is 8 x 8 and there’s an upright size which is either 8 x 10 or 8 1/2 x 11 and there’s an oblong size which is usually 10 x 8, meaning that it binds on the 8-inch side.