Making projects with kids is great for both teaching and bonding. I have done many projects with son and daughter and it is amazing how much they learn. 6 years old is not too early to start, it really depends on the child - just watch his level of interest and react accordingly.

The biggest thing that I found about working with kids is that their attention span is very short. Anything that takes more than half an hour is "long" to a child. They also may get apprehensive about making a mistake and messing something up.

Rather that getting them directly involved with the main project I set them up with their own project that they can work on themselves. That way, when you continue to work on the kayak when your son has gone to bed he won't feel that you have "gone on with out him". What ever operation I am doing (within reason - hammering, drilling, sawing etc.) I set them up to do the same on a piece of 2x4 using hand tools. We work in the shop together and, a couple of minutes at a time, every now and then, I ask them to "help" me by doing things that they are capable of. In that way they don't feel crowded when you need to "help" them when they get a bit frustrated if things don't work as well as they want. Show him what you are doing and ask for his input (providing you aren't taking him away from his "master piece"). Answer questions directly and briefly using proper terms.

Don't expect to make any real progress on the kayak when your son is in the shop - he has to be watched - but give him space to learn. You will probably end up with some interesting pieces of "modern art" - unfortunately it won't stick to the refrigerator!