I'm a parent. My daughter isn't old enough to be an activist, but perhaps when she is, I won't get in her way if she wants to reprimand the real villain in this: Congress. McDonalds may be big, they may be sleazy, but they cannot force you to pay for their food. Congress can and does force you to fork over a chunk of your wallet to titanic agribusiness ventures (like the chronically revolting Archer Daniels Midland) to the tune of $19.5 billion in FY 2014.
Non-euvoluntary exchange over a greasy fast food counter is one thing. Being fleeced by the tax collector to line the pockets of insanely wealthy plutocrats is something else entirely. Hannah, if you read this, I urge you to concentrate on the real villains here: corn processors and their pet legislators. The food from McDonalds comes from somewhere. Find out how it gets from the farm to the Happy Meal box and see what's rotten on the way. You might find that you're fighting the wrong battle.