Kristen’s Keys on YouTube (Kristen Puttagio) – https://www.youtube.com/channel/UC9EkPb6v189kT17bzHpUIjA
There are a few lessons on there but they are great to have your child learn the keyboard. My daughter learned them in the first lessons (after unsuccessful paid music lessons).
www.hoffmanacademy.com – There are 60 lessons on the site. He has been making changes to his site and looks like he is going to start charging but right now it is still free. My daughter is almost done with the lessons and does them without complaining.
www.dsokids.com – Allows you to listen to various instruments. In addition there are games on there to help you learn more about musicians and to build your own instrument.