The seller has made a mistake sending the item to the wrong buyer.
Go to the items you have recently purchased, and click on those sellers listings. In the left sidebar click on sold, and see if you can find those children's books.
If you do, you can send the seller a message for them to send you money for a tracked return postage to send the item back to them, do not be fobbed off with sending it to the correct buyer. Perhaps a family member, friend can help you with the posting.
Or, repack it, if there's a return address on the back hand it back to your postie in the morning explaining incorrect delivery.
@marmcmi-6