Fun with a Speech Impediment

I can't recall if it started before or after Ian got his new pedi-partial (fake tooth) put in, but he has the hardest time saying the "ch" sound. Now with his obsession with cars, trains, and trucks, we tend to hear the mistake very often. We've tried getting him to say, "Ch ch choo choo train", and he always gets the "ch ch" alone; but never the train. The funny thing is that he substitutes the "ch" sound with a "f" sound. It's not so bad when he says train; but when he's talking about trucks, heads turn! The first time we were driving home from church and Ian looked out of his window and said, "Wow! Look at that big *uck!", Kerry quietly looked over at me with eyes the size of half dollars. "I know, he can't say truck," I told him. Usually the big "bubbas" ignore it, understanding what Ian is trying to say; but if not, we very seriously tell them not to make a big deal about it because he just can't say the word right, yet. Now as mature as we might appear on the outside, on the inside Kerry and I are turning into 12 year olds. We've heard about so many different kinds of *ucks and sometimes you can't help your mind from "going there". I told Kerry that a comedian could create an entire set based on it. So far there have been: big *ucks, little *ucks, fast *ucks, old *ucks, fancy *ucks, wobbly *ucks, broken *ucks, fire *ucks, monster *ucks, and every color *uck you can think of. We'll secretly enjoy our childish entertainment while it lasts; I'm not ready for open mic night.