Very young. Definitely primary age. I didn't recognise them, so they don't live in the immediate vicinity.
First, I was surprised at my initial reaction at seeing children walking up my drive. I felt sure something must be wrong or that they must be up to no good. It's occurred to me now that it's really very unusual for children to knock on my door, whereas when I (and my DC) was young it would have been common, asking for a ball back, looking for a lost cat, selling raffle tickets or collecting milk bottle tops etc.
However, back to the point. They wanted to clean my car for "less than £10".
Would you let young children you didn't know do that?