It's simple, really.
Most words in English have the emphasis on the first syllable. Like the words 'English' and 'emphasis'. Also, 'syllable'.
Babies are smart. So when baby hears you say 'banana', where the emphasis is on the second syllable ('baNANa'), they think you're just making a funny random 'ba' sound before the real word starts. Which is 'nana'.
I explained this to somebody and he was like, "Nah, kids are just lazy" and I was like, "You're
This (the joy of language development) is at least half the reason I had a kid.
Banana from Svea Vikander on Vimeo.
*In fact, 'blueberries' is a bad example. It's a compound noun. When nouns (or in this case, a modifier and a noun) are smushed together like that, they both take a stress. This helps to differentiate their meaning, the difference between, "Oh, what a nice, green house" and, "Oh, what a nice greenhouse" (where both 'green' and 'house' are stressed and yes, greenhouses sure are nice). Basically, anything else would have been a better example. I just love that picture of SBJ with a blueberry mouth.