I don't think infants start out with fully formed characters. Christ had to start "from zero". Learning to eat solid food, learning to walk, learning to talk etc. But I don't think this means he went "From disobedient to obedient". I think that each decision -- each unpleasant choice is a fork in the road where you have an opportunity to choose disobedience or obedience. When you are napping or simply taking a walk you may not be choosing either one.
But you are right - the text shows growth - it shows progress, maturing, learning etc.
In Christ,
Bob