Reddit reviews Building the Weekend Skiff

Here.

Easily doable with a 7 year old, and if you can manage to not interfere too much you'll be surprised at how much he's actually capable of doing himself with just a little direction.

In reality it'll take about 4 weekends to build, but that's probably enough to begin with for a 7 y.o.

Also, why not make your own sails.

https://www.amazon.com/Building-Weekend-Skiff-Richard-Butz/dp/1888671106

It even has a sample schedule (4 days) for community building, and a list of materials you will have to prepare in advance. If you have more time, there's plenty of things the kids can do on the materials list.

I've built a metric fucktonne of the canoe with kids, some as young a 7, and I really don't think you have to worry about it not being interesting. The act of building a boat is enough, so keep it simple and go with plywood.

You'll probably learn more than they do.

Start simple. There's a sailing version in the book.

Don't get too bogged down trying to choose a plan. There are literally thousands, they all claim to be the best/ easiest/ cheapest etc. and it's quite possible to spend the rest of your life looking at plans and daydreaming.

Just jump in and do it.

I'm a boatbuilder AMA, if you want.

The first boat I built in high school was the weekend skiff . A simple boat which turned out nice and the directions were easy to follow.

I also built some simple open, single person, kayaks with a group of kids for a summer camp that was from two sheets of plywood. I don't have the plans anymore but those were really simple and the basic boat could be made in a week course with teenagers.