Rare to see something official from Disney for free like this. It's a young adult novel, not a little kid's book called Conceal Don't Feel. It's part of a Disney series called Twisted Tales where the characters have a 'what if?' difference in their stories. This one is what if Anna and Elsa never knew each other? There are other books in the series from other Disney animated movies, but this one is temporarily free until April 4 via Apple Books, Google Play, Amazon, Kobo, and Nook.
All links are here -
Apple Books [apple.com]
QA Note: Direct link from Disney: Disney Books [disney.com]