Are you sure this is a good idea? Usually, when TV producers want to make a spinoff, they'll go to the original show's writers.
I think you'd have a much better chance pitching a well-written original series. And not only would Nick be more likely to accept it, but if they don't, you can shop it around to other people.
But either way, I can help you out. I have years of experience writing voice-overs for radio and comic scripts, and I'm currently working with a team that's developing an animated web series for the 10-13 market.
Thanks for your time.