Babies learn language in a way I never remember learning anything. Having nothing to go on, it's clear they understand words and phrases before they can make their tongues say those words and phrases. And when they do start speaking, it's in approximations. Their brains take what they think they heard and make it a word. And that word sticks.
Much of my toddlers' unique pronounciation comes from skipping letters or syllables. Step becomes sep. Foot becomes foo. Dora becomes Doe-a. Video is vidi. Pineapple is apo. Banana is nana.
They'll often replace a letter with another letter that's easier for them to pronounce. Moon becomes moom. Stop is shop. Stuck is shuck. Down is dowm. Finger is finging. Milk is mook. Spoon is a combination. It becomes poom.
Sometimes, they completely replace a word with another non-sensical word without a second thought. In this way, Blankie has become Bean. Cookie is Googooleegoo. Orange juice is O-june. I find that the earlier they come up for a word for something, the longer it sticks. For instance, my twins still won't say thank you because thank you was one of their first phrases. Only it came out like "Da daaa." So now they get confused because it doesn't sound the way they remember it sounding.
Sometimes the word they use to replace the correct word makes sense in its own way. So that buttons become dots. Dogs become oof-oofs. Shovels are spoons (or pooms, more like). The moon for a long time was a ball. Sometimes the sun is the moon, especially in books.
Many words they use sound like the same word, differentiable only to me. Hat and hot, for instance. Radio and video. Draw and drawer. Cheese and please.
I know you're not supposed to mimic their baby speak back to them, but sometimes, I find I just can't help it. If they want mook, I ask them if they want mook. When they say "HO-kay! AWW-wight!" I giggle with glee.
The baby dictionary is varied and interestingly assembled - a collection of parts that really do make sense as a whole if you let yourself think about it. I truly feel like I am privvy to something incredibly special. I get to see the mind learn as it would with no structure applied. I get to see that mind take off all on its own.