ReecePace

Firstly, keep it simple and break it down into easy-to-learn steps. Start with teaching him the basic chords and strumming patterns. Then, gradually introduce the melody of the song. Encourage him to practice regularly but in short sessions, as their attention span might be shorter. By the way, I found this helpful guide on how to play "Happy Birthday" with guitar chords https://staytunedguitar.com/happy-birthday-with-guitar-chords. It provides step-by-step instructions and chord diagrams. Check it out, it might be useful for you. Good luck with teaching your son