Certainly, they are building mental pathways. The old idea was to have children reading by the time they were eight. Long before they enter public school. When we are considering mental development we are dealing with brain cells and all of the different ways those cells are connected in all of us as individuals. Mental connections for different forms of learning are different in each of us.
Some pathways are better developed than others.
Some may never develop, some may take years to develop, there is no certain pattern. We all grow mental pathways differently and to a great degree they are dependent upon our upbringing. Just look at how certain children are treated in their home. Our public school system presents us with the most serious problems with learning. Which, aside from all the social problems, comes right down to testing, something that has run socially rampant in our culture.