Some years ago we listened to a children's audiobook which we really enjoyed and I am trying to remember what it was. I think it was by Geraldine McCaughrean, Ds1 is adamant it is by Anne Fine. Trouble is we are quite hazy about the details. It was about a boy and his friend doing a car washing business and they wash the wrong car. The owner of the car that they wash is furious because he is really car proud and he is horrified that they might not have used the right car shampoo etc. Later on he turns out to be the children's entertainer for the little sister's birthday party, but the brother and his friends end up putting on a show instead.
I don't know if anyone can help identify it for us! I'm sure that Ds2 (with special needs) would like it now which is why we are wanting to find it again, though Ds1 is grown up!