As a kid, I regularly baby-sat and also did pet-sitting to earn money. My brother mowed our neighbors lawns and also has a paper route to, again, earn money.
These days, you don't see kids doing these kinds of tasks as often as when I was a kid. This NYT article mentions that many of these types of tasks have been professionalized. And I recognize that is generally true, I have a professional dog walker, I've also at times used a lawn service, etc.
My across the street neighbors' child recently gave Snarfle a bath. Mary is in 5th grade and she is the second of four children. In the past she has come over with her sisters and all three of them have washed the dog. This time it was Mary on her own. She did a good job, washed Snarfle twice, dried him off, and brushed him for about 20 minutes. I had no idea what to pay her, so I gave her a $10 which was the smallest bill that I had. I think in the past, I've paid each of them $5 or I've given them a $20 to split.
My next door neighbor also watches Snarfle for us when we go away. As I mentioned before, we have a dog walker but we can't leave Snarfle on his own for a week, with or without the dog walker coming in twice a day. I can't put Snarfle into the doggy camp because he is just too old for it. So our next door neighbor who is an animal lover and has 4 dogs of his own, feeds and waters Snarfle and brings him over to his house at night or when he thinks he might be lonely. Our neighbor won't take money from me for watching Snarfle, but he will take it from Mr. Sam if Mr. Sam forces it on him and walks away.
I want to give him money for this service because one I can't really return the favor to even things up and two I know he could use the money. It is a dilemma, we really rely on this neighbor but it is difficult for us to reciprocate or pay him (since he resists taking money from us)