Can it be explained in a way that an 8 year old can understand?
First demonstrate that there exist limits to velocities in various situations.
Take a floating balloon and start adding hanging weights. For a fixed weight there is a terminal velocity, dependent of the size and weight of the balloon-weight system. This can be explained by the reaction of the air to the force of the weight .
Then explain the elementary particle concept, it is elementary particles that cannot get a speed greater than the speed of light. Particularly that light is made up of photons, and the photon is also an elementary particle. All matter is made up by these elementary particles and therefore no matter can go faster than c.
Explain that this limit is an observation , a measurement, and it has been modeled/described by special mathematical descriptions. For mathematical descriptions one can show triangles and other geometrical figures, a maize for example constrains motion and the constraint can be described by geometrical figures.
Go back to the balloon. We know that there is a limiting velocity because of the air and the forces . The elementary particle, if pushed/accelerated finds a resistance, not from air but from space itself. Analogous to the terminal velocity of the balloon the faster it is pushed the more resistance it finds from the intrinsic structure of the space itself. The terminal velocity for the space and time we live in is the value of c, the velocity of light in empty space.