You know my thoughts. Short course all the way. It will cost a little bit to buy I think around £250 RTR brushless with 2.4ghz radio gear. In the long run it would save money and keep interest for the smaller ones as there should be less down time, less off track time and a lot less time on the tools which for the dad's racing too will be better as fixing 2 cars between heats isn't going to happen.
I vote short course.