WASHINGTON — Anna C. Corbin had not been involved in politics, had not even been to the Capitol before this year. But since March, she has made the two-hour drive here from her home in Hanover, Pa., 15 times so her sons, Jackson and Henry, could lobby against efforts to dismantle the Affordable Care Act.

Jackson, 12, and Henry, 9, have a genetic condition known as Noonan syndrome, which causes a bleeding disorder, short stature and digestion problems. They also have a new profession — “little lobbyists.”

In the long-running battle over health care, doctors, hospitals and insurance companies have spent millions of dollars this year. But some of the most effective advocacy has come from pint-size petitioners who spent nothing at all: children with serious medical needs who told their stories to members of Congress.

“We were often told that the kids were not voters,” Ms. Corbin said. “But they will have this genetic condition for the rest of their lives. They will be voters, and these laws will affect them. So it’s important for them to have a voice.”