Originally Posted by Rina
I recommend you let him watch a video or show him how to serve instead of talking about it. It might be too much info to process for and adult(I know it is for me) and very difficult for a child. Have him watch the video right on the court and then tell him to imitate it. You are probably showing it to him as well, but if you find a player he wants to emulate that might be more productive. I read this in a book and then tried it with my son(forehand) and for the next 10 minutes his forehand was whipping and making winners like crazy. After that he forgot about it, so it needs to be a repeat process.
This I totally recommend. The most my kid learns from is watching videos. Infact even in videos he learns most from watching recorded matches of his heros, using pause and slow motion whenever he sees something he would love to hit himself. The video instructions with loads of jargon also bores him. Youtube has tons of match highlight videos of 15-30 minute duration. Each one is worth it if your kid learns visually.