Would you send your child to Math class without Math book, to English class without English book, to Science class without Science book? Of course, you would not. Then you will certainly help your child in piano lesson stay organized by having proper material at piano lesson.
Contrary to the popular belief of piano students this will not happen by itself. Proper planning well ahead is the only solution. You can help your child in piano get organized for its piano lesson, by establishing a piano routine the night before. Purchasing a piano bag is a great way to keep your child organized. You also have to teach the child how to use the bag. On the morning of the piano lesson day there should not be any piano lesson books on the piano as they are supposed to be in the bag. It has to go into the car. This way the child will have its lesson books when you arrive at the piano studio.
The most common excuse given by students for not bringing the book is that they left it on the piano. Don't just ask your child on the way to the car, "Do you have your piano bag?" Check if any books are left on the piano. The books should be in the piano bag. There is no use if the piano bag is taken to the class without any books or the right books in it.
Sometimes children will leave a particular book with a difficult song in it at home. Instead, it is better to get more help from their piano teacher. Sometimes it takes a couple of lessons before students feel comfortable playing a piece at home. By not bringing their books, children will not have enough time to overcome challenges while learning new music skills. Do not allow your child to give up too easily by leaving music book on the piano.
Generally good habits take time to develop. So, be patient. Try to inculcate Piano Lesson Book Habit. Over a period of time it will serve your child in piano lessons well and it develops confidence and achieves its musical goals.