Looking for advice....

... Cool Constructing Kits for my younger son Gabriel. He's 7 -- but is considerably older than that with respect to mechanical understanding.

I'm looking for something on the order of the K'Nex, etc., but with more operating components to permit him building things that operate more realistically and more complexly. I'm not sure if the new Erector sets would really do it or not, or if there'd be a better choice. Especially considering the other kids in the house.