Children Learning Language

During our last couple of class discussions while we've been talking about how children learn language I started thinking about my cousins. I have 7 cousins and have been around 5 of them since they were born. With the first three, who are now, 17, 11, and 5, I can remember them making up words and making the mistakes we've been talking about in class. However, as I think about my youngest two cousins, who are twins, I can't help but see the differences of how they learned to language. It seems that they too made up words but they didn't do it as often or for as long as my other cousins. I think that maybe had something to do with the fact they were always around older children and tried to copy exactly what they were saying. At the age of three it is so much easier to understand them than it was to understand their sister at the same age.