Squeaky Voices

Is it wrong to laugh, usually under my breath, when I hear Justin and his friend getting all into their video game saying things like "Dude!" or "What're you doing!?" with a nice squeak in the middle of each syllable? Or sometimes the squeak is at the end of the word. Sometimes you can't hear it but others it's so obvious it just makes me laugh. Just now it was a whole series of "Dude!"s and every one of them was squeaky. I of course, being the considerate mother that I am, leave the room before I laugh or I hold it in and try to keep the smile on my face to a minimum whenever I'm close by but really, it makes me giggle.