Get him a board. Mine started when she was eight but she is really small, she is ten now and only 4'2'' I bought her a 5'10'' fish to start with and it was ideal, really stable so she had plenty of time to get to her feet etc. She just dragged it out by the leash until she was about chest deep. She has now got one of the salomon noseless boards the 5'. She finds it a lot easier to paddle than the fish being a bit narrower, it is a challenge for her though. But be warned you will spend a lot of time pushing your littlun into waves as well as spending time knee deep watching them with a big grin on your face that will stay with you all week.
They make some really good kids wetsuits, got mine an Alder winter suit and she kept going right through Jan and Feb last winter.
Where abouts are you based? Filf in Rottingdean do some great kids stuff, give Steve a call (and I might have a fish for sale soon).
Here are a couple of Daisy , the first one is her on the fish, being small they get going on the smallest ripple, the next one is a day I went in with her because she wanted to try some bigger waves.
Sorry for the long post but surfing with your kid is just the best
