A few years ago I had a carpenter install countertops in the kitchen I was remodeling, but I shouldn't have let his assistant install the sink. He bought a whole bunch of PVC turns and twists until he could get the pipe to go from point A to B without cutting anything. It leaked and after a while rotted out the board under the sink. I called a plumber who looked at that inquiringly, and I explained "a carpenter put it in." Good laugh for him and he fixed it. An English professor friend was visiting a few weeks later when I still hadn't gotten around to replacing the board below the sink yet, so he did it. Works great.
Carpenters and plumbers and electricians are always interesting to small children. I see no reason why they shouldn't watch, as long as they stay well out of the way, or possibly make themselves useful. And I stick around to watch and learn, or to keep an eye on things. I sometimes will leap on neighborhood opportunities to save a few dollars. Next door was having some plumbing done when I needed both outside faucets replaced (the washers were leaking, but the faucets themselves were so old they were hard to work with, so I wanted both changed out so I can again change washers myself). I trotted over at lunchtime and asked the plumber to step next door for a minute, and explained what I wanted. After his first job was finished they came over and did it for less than the basic service call.