'Machines, tubes, wheelchairs'. Georgetown short answer.

In the space available discuss the significance to you of the school or summer activity in which you have been most involved.

Machines, tubes, wheelchairs. Walking through the halls of Children's Hospital was depressing-until I met David. As a hospital volunteer, it's hard to see sick kids. I get emotional playing with the three year old girl, strapped down in her wheelchair, unable to move. I tear up when the little boy screams at the sight of the needle. I cringe when I see a tube sticking out of a toddler's mouth. And when I met David, who lived with a sac-like apparatus outside of his body, I felt the same way. I'm not sure exactly what was wrong with him. He had trouble speaking and walking, he breathed heavily and would always lift up his shirt to show me his impaired stomach. But seven year old David wasn't sad. He never complained. Each Friday he greeted me, at four p.m. sharp by the elevator on the third floor, holding his younger sister's hand just as all big brothers do. He would walk in, smiling, ready for the new day. It didn't matter that a bag protruded from his stomach, that he couldn't talk, that he was different. David was perfect and loved life. I haven't seen David for months. I'm not certain where he is now. But whenever I stand by the third floor elevator I'm reminded of his impactful presence. Because of David, walking through the halls is no longer depressing, it's inspirational.

Am I completely off track??

I think this sentence might be unnecessary.

Overall, you are still on the track, but you'll have to say more about how David is important to you, and link the experience with the summer activity--- what did you do with David. Just get back to the assignment and make sure you wrote what is required.

I actually think you should keep the sentence about how you react to seeing the sick kids-it makes the essay more relatable. Overall this is really good. I agree that you should expand a little more on what you were doing at the hospital and how it impacted you, and maybe also talk about how it's changed your perception of sick kids (you touch briefly on it with your last sentence but I think it could be a lot more powerful if you delved into that more).