How to include a song with a children's book?

I wouldn't worry about limiting it to people who purchase the book, assuming you own all the rights to the song/performance.

I'd give it away. Hope that popularity of the song drives sales.

So I'd put a link in the book.

You could use a code word as a log in (the third word on the fifth page, a character's name, etc.) or a QR code, if you wanted.

There are free generators for printed or digital QR codes.

My wife runs a local toy store which has a good-sized book room, and I'm pretty sure there are books in it with included music. I haven't actually paid much attention to such, but you might want to hit up a bookstore and see what they may have.

caw

I suppose you could include a website link in the book itself. If you do that, make sure the link is very easy to type out. Nobody wants to type out a super long URL.

I think they still use CDs in books. But you can Google book with CD and see what appears as well as checking local stores.