We do something very similar as part of our summer camp. Each kid spends two days (for a total of 4 hours) at each station. It's not as focused as yours sounds - we spend time talking about the robot and how the electrical system goes together as well as making the our own kits (the camp is for prospective members, not just anyone).
We get our kits from
http://www.apogeekits.com/ - I've had an excellent experience with them every time - twice now the kit we had at the top of our list wasn't available in the quantities we wanted, and they offered a different (more expensive) kit at a discount to match the price of the original order. (Note: I have no affiliation with them other than as a customer with 3 orders over the past 3 years)
We have the kids practice soldering initially with small scraps of wire. They typically end up making themselves little "electrical bracelets" with different colors of wire they can wear the rest of the camp.