Bennyw,
First, I honestly think you're onto something here! Your solution to what I think is a common issue-- i.e. what to do with the child and their bike when they can't keep the pace, are tired, or conditions are unsafe, etc.--- looks simple, effective, and unique.
Furthermore, that you've managed to acheive those things and a competitively light weight using basic materials and manufacturing (it appears; correct me if I'm wrong) really augers well for continued development for commercial purposes, I think.
I would really like something like that if it looked right (sophisticated, finished), worked well, was built well, and was easy to install/remove. Of course it would need to be priced right, too, which is probably somewhere in the $100 -$150 range, but that's just an off the cuff number based on a few, gross assumptions. If it turns out that there are additional features like the ability to fit standard panniers, or maybe a proprietary luggage system that allows bags to be moved off the rack to the child's bike while towing, the value assessment may be higher.
In sum, wow! Great work! Now the question is one of where to go from here. If your inclined to consider the possibilities, it may be worthwhile to seek a patent for starters. That'd be handy in just about any scenario, whether you manufactuer on your own or want to license the design.
Finally, if you are interested to develop the idea, I'd be keen to help and offer feedback. I don't have much to offer in the way of capital investment, but perhaps having someone to help test, purchase a couple of prototypes to help defray costs, and provide some thoughtful feedback would be helpful. Message me if you'd like to talk about any of that.
In any case, I'd love to see more on how you put this together and how it works. Could you lift the front wheel into the carrier rather than the rear?