There is little difference in people, but that little difference makes a big difference. The little difference is attitude and the big difference is whether it is positive or negative. It's not the aptitude but the attitude that will determine one's altitude in life, at school, or at work but this applies especially for children. This starts with the attitude towards themselves and this then impacts their attitude towards others and the outside world.
The inner fire and drive is the most important thing to possess for any accomplishment in life and we nurture that kind of energy in budo. When a class powers up in energy, working together on a kata or a basic combination or fitness, it rubs off on everyone in the class. Young students feeling this energy will absorb it and over time will become able to do it within themselves. This is how the capacity for response is built. In a self defense situation or facing a challenge, most react in fear and stress out. A response with a positive attitude and appropriate energy is much more effective. This can be learned and trained. So if you see or hear a high energy kid's class and you wonder what's happening, now you know the goal.
Learning and thinking while moving is a really valuable skill, especially when achieved in the noise and power of a group. Children (as adults) need to express their energy and kids especially have lots of it, and once settled it can be molded into a powerful force for action.