By chopping all of your vegetables to about the same size, they’ll cook more evenly (and be easier for tiny mouths to eat!)
How long to cook vegetables depends on their density. What’s density? It’s a word that describes how hard or soft something is. Raw carrots are hard (kind of like bricks!) so they need to be cooked for awhile to allow the heat to get all the way to the middle. But vegetables like tomatoes are soft (like pillows!) and only need to cook for a few minutes.
Why do we do things in order, like put our socks on before our shoes? Is growing up something you have to do in order? Why?