Why do children have smaller hearts?

Children have smaller hearts primarily due to their overall smaller body size and the developmental stage they are in. As children grow, their organs, including the heart, also grow to meet the demands of their increasing body size and metabolic needs. Additionally, the heart's size is proportional to the amount of blood it needs to pump, which is less in children than in adults. As they mature, their hearts develop further to accommodate their larger bodies and more complex physiological requirements.