Something to think about is maybe suggesting that you invite 1 or 2 friends to come along and have your parents drop you off at the expo and then they can go do something that interests them for a while and come back and pick y'all up. Since you know what your parents are into, before even suggesting that, try Googling the "tourism" or "planned events" web page for the city that the expo is going to be in and see if there are any events planned for that weekend that your parents might enjoy, and offer that as an idea that they could do while you were at the expo. Just a thought...