I did a little digging and found a post on Quora talking about it. It stems primarily due to how intelligent the child is. In most cases a lot of children experiment with words and their vocabulary when they start learning about words. They’ll start with one word sentences Eat, sleep, dog, mommy, daddy, etc. Eventually by the age 2 roughly you’ll know some more words and you can make some sentences like “Have drink?” and such. And that’ll continue until they form proper sentences. Lower intelligent children will talk slower and will take a bit longer than average to go through those stages. However an intelligent child is basically familiar with this process. They will actually wait until they get to the later stages, stages where they can say proper sentences. They know this because as a baby you spend your time with your parents and other people who are speaking english fluidly. Einstein was that case because he basically thought “My parents and adults around me are speaking good english but I know I can’t talk properly right now. I’ll practice more until I can speak like them.”.