How soon do you expect to put him on his own board?
I teach lot's of kids of about that age, and if you get an appropriate rig that he can
uphaul, he could be sailing very soon. (actually next week)
A small GO board, or better still one of the Starsurfers or Kiddie boards with a 2.0 sq meter(or larger if he's larger) rig and he will be sailing along right next to you.
I use some other techniques that give the tiny sailors full control, without putting them in any jeapordy.
First, how big are you (i.e. what is your weight).
With a Start or Rio, (M or L) you can kneel on the front of the board and help with the uphauling, but once the rig is up and balanced your 6 year old can do all the sailing.
When he is able to uphaul, tack, stay upwind, flare jibe, etc. (usually in a day or 2 on the water) then you can use the bungee tether.
This puts your child on his own board and completely on his own, but you are sailing just in front of him.
Make it a "challenge".
Tell him his new task is to keep "slack" in the tether line.
Usually takes about 5-10 minutes for a kid to figure out what he/she needs to do to keep slack in the tether, then you can untie the tether and just sail along together.
The real "critical issue" here is to get him a rig that he can handle by himself, and if you are tethered, or sailing together, get yourself a similar size rig.
It does not work if you are constantly "towing" due to you having a much larger rig size.
I use the Sailworks Retro Ripper rigs (probably the best kids rigs available, anywhere) and select a rig size based on the chllds ability to uphaul the rig.
Then off we go out onto the water.
Since I'm doing this with kids at "A Taste of Windsurfing" events, I have to be alot more careful not to exceed the childs strengths and abilities and put them in some sort of "out of control' (dangerous) situation.
So, I check the condtions, select the rig, and decide if I'm going to be riding on the board with them, or putting them on their own board with a tether.
I often ask the individual kid what they would rather do. The timid ones want a "ride along", and the bolder ones want to try it "all by themselves". If I find they are much better than they thought they'd be, we switch to 2 boards. If I find that they aren't doing well on their own, we drop off one board and I ride along. Everything about teaching kids to windsurf has to be dynamic/situatiional.
All the kids I teach get a 5-10 minute session on the simulator so they understand how to uphaul correctly, tack, steer and all the other "basics".
The most important "basic" is learning to balance the rig.
Once they can balance the rig, they can sail for quite a while as they are no longer holding the rig up, because it's balanced over the mast foot.
Be sure to pick your conditions right at first.
If you send him out in intimidating conditions, before he's ready to challenge stronger rougher conditions, he may develop a fear of windsurfing that will be hard to overcome later.
The most important thing for small children is to understand their shorter attention span, and do everything you can to make windsurfing easy and fun.
The more fun, the better.
Don't be discouraged when he decides that it's more fun to play with other kids on his windsurf board, than it is to sail it. He'll get beyond that fairly quickly, but always remember he's a kid and needs to play and have fun while he's learning new things.
Let him learn at his own pace. Do not pressure or push him to do things he thinks are too challenging.
Little boys love a challenge, and as long as he's having fun and feeling challenged there's no limit on how quickly he will progress and how much his skills witll develop.
Again, keep it fun and get him a rig that he can handle. These two points are absolutely
If there aren't other kids at the beach, change beaches or bring some other kids with you.
Hope this helps,