Capt. Dave...I too have raced with a young son, from his age 6-11, first on a Hobie 18, then a Nacra 5.5 SL, then the F18HT Bimare Jav 2, then the Inter 20. A couple things I would recommend. First, get a self tacking jib. The loads on the jib sheets when it's blowing will be too great for a youngster (or small woman if you are lucky enough to be sailing with one

) so that will help quite a bit. Second, if you are getting a spinnaker boat, rig the halyard so it is very easy to raise and snuff, and think about you being the one doing it with one hand while trying to drive with the other, so make sure you can reach the halyard and sheet from the back seat, unless you intend to let him drive. Three, pick your conditions before you leave the shore! If there is a big wind and a high probability you will crash, stay on the shore. If you are already out and it really starts to blow, go in. I can tell you from my experience that if you go out and he gets washed off the boat, or you do, or you both do and get separated from the boat, or he sails away without you, or he falls off while trying to hook in and get out, and you run his legs over with the rudder, or you stuff the bow and he fly's around the forstay and hits the lee bow head first (we did it all) it will be a long,long time before your wife let's you take him out again! And no amount of cake and ice cream on the way home will keep his mouth shut after you leave for work. She WILL find out.
In light air you two will be great. In medium wind you should be be ok, but in heavy wind, see if you can swap him onto the committee boat with a camera, and you get an adult in exchange. My son loved driving one of the rescue boats at one regatta when I had to replace him due to high winds, he was able to help rescue a couple of boats and had great storys to tell, wich is a better outcome than thrashing him while crewing on the cat.