I use Pinterest to find songs. At first I looked for simple songs that I knew that had only two or three simple chords. I would practice those easy songs over and over until I could do it smoothly. Then I would add another chord or two and a couple of new songs. To start simply builds confidence. I wouldn't start a 5 year old out with a teacher who would want to teach scales and music theory or how to read music. That can come later after they have become hooked on playing music. YouTube is also great for learning strumming and the can play along. Look up something like easy beginner ukulele songs for kids. Good luck!