[Oliver]

Nanny
Like the hippie above and the funny hairdo guy  ...  one thing I have found is the kids can get a bit impatient so we now we plant fast growing crops like radish.

They also do allotment things with kids from the local school.
By all means grow some fast growing things, but it is important that kids (as well as some grown ups!)  learn that life is not instant so some 'normal' things like runner beans and squashes and pumpkins  are also important. Everyone grows 'the tallest sunflower', but kids also need to learn that not all sunflowers are tall. Some kids like the multi-branched flowers that they can pick. They all grow fast enough, especially when the kids come back from their hols and they see a difference (if the weeds have not hidden everything!)