When looking at what makes a trampoline bouncy we need to take a step back and understand the science behind trampolines. Energy conversion and storage is the key to a trampolines bounce with potential and kinetic energy the most important for trampoline science.
Potential energy is stored energy ready for use. Food is a good example of potential energy, your breakfast has lots of potential energy stored in it ready for you to use during the day. Electricity is another form of potential energy we use it every day. Trampolines store potential energy for us to bounce with.
Kinetic energy is movement. How much kinetic energy you have is a combination of mass (weight) and velocity (speed). If your kids are moving slowly they have very little kinetic energy, think how easily they stop. Now mention food and see how much kinetic energy they gain and how hard it is to stop them.
While on a trampoline your total amount of energy is the combination of your kinetic energy and your potential energy.
Total Energy = Potential Energy + Kinetic Energy
E = PE + KE
As energy is never wasted, it is simply converted between different types so that the total energy remains the same. The trampoline, gravity, and yourself all work together to convert your energy back and forth between kinetic and potential energy.