1. "Dop it!" instead of "stop it!"
It's not easy to start a word with a consonant cluster. Kids don't have the fine motor control they need to produce the 'st' in stop, but they don't just leave it out. They substitute a sound they can produce. 'D' is a very smart substitution for 'st' in "stop." If you take a careful look at the acoustics of 't' in adult versions of "stop" vs. "top," you see that the 't's in those words look different from each other. The vocal cords kick in sooner for the 't' in "stop." A 'd' is basically a 't' where the vocal cords kick in sooner, so when children substitute that sound, they show they've heard the difference between "stop" and "top" and hypothesized that it's important for the language. And they are right!
2. Calls the dog "baby."
When children start using words, they haven't figured out all the situations in which they apply. They form hypotheses about word meaning and apply them on their own. The child might call all the kids and pets in the family "baby," but not the parents, revealing a hypothesis that "baby" means "family member who other people have to get food for." She may call everyone she meets "baby," extending the hypothesis to "living creatures." Like any good scientist, she can only confirm her hypothesis by testing it. Eventually, she will get enough data to settle on the right one. (...)
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