It is written in the Talmud: "One who visits a person who is ill takes away a sixtieth of that person's pain." The mitzvah of Bikur Cholim (visiting the sick), a Jewish tradition to support those who are sick, can be traced back to the Torah when God visits Abraham after his circumcision.
This mitzvah can be performed with children starting at an early age. Young children remember being sick, so they can easily empathize with another person.