Just use plain visitor's

excuse. Thousands of thousands of parents got their visas just because they wanted to visit their kids in the States.

No need to complicate things using extra excuses.

I knew a friend who suffered from brain tumor. Her parents were working in Denmark, one of them was a doctor. She went there to apply for her visa telling them that she was going to to have the operation done there. The VOs had a long discussion and finally refused her visa. But for pure visitor's visa, it is a lot easier. She wanted to get the operation there, but the real reason scared the VOs. She ended up having it done in Beijing.

Just FYI. I don't see any need to use that as an excuse. Pure tour purpose is good enough.

Good luck.