Is it safe for my kid to knock on doors?

With rules, yes, and the rules are short enough for a kid to actually hold in their head.

Daylight only. Including the winter afternoons that get dark at four thirty.

Streets they know. Their own block first, then the ones next to it. Familiar streets mean familiar faces and a short walk home.

Never go inside. The whole conversation happens at the door, every time. Worth stating as an absolute rather than a guideline, because an absolute means a kid does not have to make a judgment call while somebody friendly is inviting them in.

Somebody knows the route. Which streets, roughly how long.

A way to reach you. If they have a phone, it is with them.

Go with them the first time, and stand at the sidewalk rather than at the door. Visible and uninvolved is the entire distinction. Standing at the end of the drive while your kid does the talking is support. Doing the talking is taking the business away from them.

Younger kids should go in pairs, which helps with nerves as much as safety.

Practice an exit sentence before the first knock, because a kid who has not rehearsed one will freeze if somebody is odd or pushy. Thanks anyway, I have to get going, said while already stepping back, works and needs no explanation.

Then the rule that sits above all the others: a bad feeling is enough. They can leave any situation without being sure, without justifying it, and without worrying about the money. Say it out loud and mean it, because a kid who thinks they will be in trouble for walking away will stay somewhere they should not be.

Worth knowing: the risk parents picture is a stranger, and the things that actually go wrong are equipment injuries and property damage.