I'm blessed with a father who is an engineer, so luckily for me I didn't have to worry about this. However, I would like to offer advice, despite not being in the same boat.
Try going from the other angle. Instead of trying to convince them that robotics isn't going to hinder your chances of getting into a good college, try telling them that
not being in robotics could hurt your chances of getting into a good college. In the US, the ACT's and SAT's are being taken less and less seriously. Instead, colleges are looking at extracurricular activities, and the compitition is feirce. FIRST is great for college applications, because it shows ambition as well as intelligance and stuff. Not doing anything but focusing on your core acidemics can accually hurt your future. It's not that doing robotics can help your future, it's that not doing robotics can harm it.
