Here's a quick excerpt from the late Douglas Adams' book "The Salmon of Doubt" that struck me as particularly amusing (being the parent of at least one youngster who has troubles with the letter "R").

Here are two more things you should know the difference between: road and woad. One is a thing that you drive along in a car, or on a bicycle, and the other is a kind of blue body paint that British people used to wear thousands of years ago instead of clothes. Usually it's quite easy to tell these two apart, but if you find it at all difficult to say your r's properly, it can lead to terrible confusion: imagine trying to ride a bicycle on a small patch of blue paint, or having to dig up an entire street just to have something to wear if you fancy spending the evening with some Druids.

With that in mind, imagine me trying not to giggle while telling my son to look both ways before crossing the road...