Explain Ionizing radiation as a twelve years old kid.

Ionizing radiation is caused when a very heavy atom emits a particle at the speed of light called ionizing radiation.
On contact with a material, either the atom absorbs the ionizing particle or 
The ionizing particle breaks the atom in two and forms two ionizing particles which can create a chain reaction.
There are three kinds of ionizing particles: alpha, beta and gamma
Alpha particles react a lot with matter but travel a very short distance.

Beta particles react less than alpha particles with matter but travel a very short distance. 
Alpha particles react less than alpha particles with matter but travel a longer distance than alpha particles.

Gamma particles react less with matter than beta particles but travel a longer distance than beta particles.