An adult neighbor maybe, assuming he was already mowing his own lawn. I would offer to pay kids, however. If they refused payment, I would offer to take them out for an ice cream or a burger. I'm not looking for anything for free, especially from people that have less than I do. I remember visiting Kenya and seeing locals on the dock bartering with first-world tourists, who were trying to get the best bargains possible from them. It just seemed wrong to me for people who could afford to go on a cruise and camera safari half-way around the world to try to see how little these people would take for their labor.
What I wouldn't do is what you said you'd do, which I don't consider analogous. You said that you would take money from others to pay a debt that you could afford to pay yourself. I wouldn't. As I said, we have different values. You're a conservative. I'm liberal, a progressive, and a humanist who tries to live by the Golden Rule. We have different psychologies and view our duty to others differently. Life's been good to me, and now I want to share because I can and it feels good. I put up two extra solar panels just to send the excess power to the utility to help power other homes without burning their fossil fuels to generate it. Why? Because I can, and consider it good stewardship of the funds spent. That was a couple of hundred dollars a few years ago that's still giving.