Character Studying

Well so far, my idea of what the characters are going to be hasn't really changed all that much. However, their are a couple of things that I want to add to their characteristics. For example, the activity that we did in class today inspired me to add that Mateo Phillipe Raphael Batista the third is actually very impressional and pretty much agrees with whatever he is told regardless of how out of the ordinary or rediculous it is. Currently, Mateo is a five year old Filipino who attends a public elementary school and though he is very young he swears that he knows everything. The grandpa (Mateo Batista senior) is your typical elderly war veteran. He is very opinionated and over time, he has passed down his biased opinions to his younger grandson.
I have been trying to find the best way to show the growth that mateo goes through as an individual as well as an independent. However, I have come to realize that it is in fact quite difficult because considering his age, people just don't change mature that rapidly. On the other hand, Yomi, the Japanese five year old is the exact opposite. He is shy but he thinks on his own two feet and doesn't agree with everything hears which allows him to gather bundles of imformation then later come up with his own opinion and ideas. We need to come up with some more events that will occur throughout the story though, because our story lacks some exciting events. We also need to some how incorporate and tie in some more emotion into the characters without changing their entire personality.