Final answer:
Children's heart rate decreases and their blood pressure increases as they grow into adulthood due to changes in body functions and arterial elasticity.
Step-by-step explanation:
As children grow older, their heart rate becomes decreases and their BP (blood pressure) increases. So the correct answer is a) Decreases; increases. During childhood, the heart rate is higher due to the faster metabolism and growth processes occurring in the body. As we enter adulthood, the metabolic rate stabilizes and growth slows, which means the heart doesn't have to work as hard to maintain the body's functions, leading to a decreased heart rate. However, as the arteries may lose some of their elasticity and other factors such as an increase in body size can contribute to an increase in blood pressure.