Project Resource for Teaching Tools

I was browsing the internet looking for ideas for a project for my nephews to make over the summer when they visit. Complicated enough that a 13 year old would be interested, simple enough that I could help the younger kids in the neighborhood through it as well. I started off thinking about either a pine car derby or CO2 cars. Then I found Kelvin Educational. This sight has good prices on pieces if I do decide on cars,, but they have a lot of other cool things too, many geared towards classroom use. Bridges, cranes, catapults, hydraulics, robots, they have a bit of it all. Certainly a resource to use when thinking about how to teach concepts of engineering within the classroom.