If you don’t mind a learning along with your child approach, I may have a book recommendation for you. I started teaching beginner piano to a girl this year through a private lessons program that a local Christian school and my church’s homeschool co-op is sharing, and the coordinator suggested I use this book. It does a nice job of easing you into familiarity with the keyboard and reading music, and there’s also an accompanying music theory book you can get to reinforce things.
For the record, I did already know how to read/teach music going into this, since I studied piano as a child, I was a flute performance major in college, and I’ve been teaching that since my sophomore year there. So I’m not sure how teaching out of this book would be with less music experience. But I hope that helps!