The different functions develop at different stages. If I remember correctly, a child will first develop SFP. This lines up with Pageat's stages of moral development where good and bad is determined based off the consequences. Good provides good consequences, bad provides undesired consequences. Immediately following that stage is the stage where good or bad reflect their parents desires. They are sensitive to what the parents want and will do the "right" thing because it makes mom happy. This is still under F. They haven't developed N at that point, so they aren't capable of the abstract thought required to understand just why things are good or bad, or have a reason beyond what is concrete. This also goes along with the monkey see monkey do stage of learning, where they will simply copy and mimic what they see those around them doing. Having not developed N, they have very poor problem solving skills on their own. J is typically next to develop, so you'll see most children go through a stage where they have to do things or have things a certain way and they might get mad at you if you deviate, even if it's easier a different way. N and T are the last things to develop, however I don't remember in which order they typically occur.
The functions are not set in stone or hard wired as if to say, this is the way we are and HAVE to be from birth. As a child's brain develops and becomes capable of more complex thought processes, the different functions will develop.You have to develop the ability to use the functions before you can settle on a preference. Children may also "flip flop" functions as they're developing.
So to answer the question, no, not all children are ENTP's, no child develops as an ENTP initially, and you won't see a very young child being ENTP.
