Well, most kids and adults, for that matter, love to break boards for various reasons. If you ask a child, they would say "because it's cool" and an adult would answer, "it shows their strength physically and mentally". In general, breaking was used both as a method of measuring force of strikes, as there was no other way to do this until recently, and as a measurement of mental fortitude, the ability of the mind and body to overcome obstacles.
Generally, a martial artist engaged in breaking practices will practice by hitting something hard. A famous breaker who was known for breaking the horns off bulls, would use trees. Martial artists would also use other hard surfaces to condition themselves prior, not always for simply breaking, but so they could withstand the strikes associated with breaking. They build up their bone density, muscles and the skin.
Also, many Chinese systems also are of the school of thought that "internal energy" or Chi is used when breaking, which is not dependent upon muscle strength and body weight, but by the energy found within the body. In today's martial arts classes, board breaking is simply done for demonstration purposes and to show strength in some instances. It gives the child a sense of accomplishment and it really does boost their self esteem. You would be surprised what a little piece of wood can do for a child. Plus lets not forget "it's really cool." As always, you can reach me at Cervizzis@aol.com.