My 4 year old finds it hard to pronounce 'pl' and says it more like 'cl' as in clug and clum instead of plug and plum. He can just about say it when I get him to listen carefully but then lapses back into saying it wrong. His hearing has also been a bit dodgy recently and I'm worried it might be linked. I've made an appointment with the GP for in a couple of months. Is it a difficult sound to say? Should I be concerned? Other than this his speech and vocabulary is excellent.