Should a kid help another kid who competes with them?

Usually yes, and it is less noble than it sounds. It is mostly arithmetic.

Another kid starts doing what you do on your streets. The instinct is to drop your price, and a price war between two kids has one ending: you both do the same work for almost nothing and neither of you gains a customer. The person who leaves you over two dollars was never loyal anyway and will leave them the same way.

Talking to them opens options that fighting does not.

Split the streets. You take this side, they take that one. Neither of you crosses town, both of you get density, and density is what makes these businesses work.

Cover for each other. Somebody is away or sick, the other one covers. That way neither of you loses a customer to a missed Saturday, and missed Saturdays are how customers actually get lost.

Pass on overflow. When you are full, sending work to them costs you nothing you could have taken anyway, and it comes back.

Two kids who coordinate both earn more than two kids who undercut. The customers do not lose either.

There is also the version where the other kid is just starting and struggling. Answering their questions costs you an afternoon. What you get is somebody to send work to when you are full, and a reputation that travels further than anything you could say about yourself.

Where to hold a line: you do not have to hand over your customer list, and you do not have to help somebody who has been dishonest about you. Being generous is not the same as being a pushover, and a kid who cannot tell the difference will get taken advantage of eventually.

The simplest version of all of it: an open hand fills faster than a closed fist, and in a neighborhood that is a strategy rather than a sentiment.