Step 1: Finding inspiration

So, there you are. You’ve written a good story and have great visions of getting it published. So now what? How to turn these words into a book?
My advice is to start with taking a trip to the bookstore. Seriously. A physical trip to the bookstore (obviously with COVID, this might be impossible, and then you’ll need to improvise). Seeing physical books on shelves and being able to touch them, feel them, smell them is a gift to anyone who wants to make a book. 
Look at books that are similar in content, length or have a similar target audience to the book you want to create. Hopefully one of the ones you pick up will speak to you, and you’ll be like, “This is it.” Or maybe it’s a couple of books – the size of this one, the binding style of that one, the paper in a third.
Then get intimate with the books you choose – take photos, write down their names, get their numbers, measure the size (you might need to buy the book first). 
I have a large collection of children’s books and I often browse them when I’m searching for inspiration.
What you are hoping to come away with after this exercise is:

1. Your book size
2. Binding 
3. Paper type

Page size:
You need to choose something that works with your printing service, and also your budget. Perving over a hardcover, embossed book is one thing, but if your printer (or wallet) can’t handle it, then that’s a bit pointless.
Popular book sizes are below. The sizes are in inches, because that’s what KDP uses, and most self-publishing authors will make sure of this service (I do). For those of us in the metric system, I’ve included a standard A4 page in the background for reference. Also note that if you are going with IngramSpark, their landscape size is 11" x 8.5".

Binding:
There are three basic options when it comes to binding children’s books: 

1. Saddle-stitched, which is a fancy way of saying that the book is simply stapled together.
2. Perfect-binding (or PURR, which is similar), this is when the pages are glued together, and the book has a spine. Something to note is that this type of binding has a minimum page count of 24.
3. Hardcover, this is when the book has a … hard cover. 

If you are publishing through KDP, your only option is perfect-binding, which makes this an easy choice for you.
IngramSpark offer all three binding types, as will most traditional printers. The type of binding will naturally affect the cost of printing.

Paper type:
KDP does not give you options for the interior paper type – which will be white bond paper (the same as your printer paper), so another easy choice. IngramSpark does offer glossy paper options though.