Greetings fellow Teacher. I would like to take your offer but a few things are a little vague.
"I would like to have a demo that I can show to perspective clients."
Will this happen before or after you pay the programmer? Also, how much of the royalties are you planning on sharing with the programmer, after you re-sale their work? Is there a chance that it wont sell, and the programmer will not be payed?
"I need a demo of a game to teach coding"
Well, it actually looks like you are making it for re-sale and profit. You clearly state that you will be re-selling this work to other clients, not for your "students" benefit at all. It looks like you will be the only one to benefit from this. ( am I wrong? My English is really bad.)
"If this goes well, I need to develop further levels and further games that will teach the basics of programming using blockly codes, and then one teaching game design."
If it is a paying gig, then it sounds really great! Do you already have potential buyers? Or are you developing a prototype for an investor?