Boston ? Massachusetts began signing up it poorest residents for low-cost health insurance Monday, the first step in the state’s goal to be the first to require all citizens to have health insurance.

“This is a historic day for us,” said Gov. Mitt Romney, who signed the state’s new health care law in April. “It’s real today.”

This summer, the federal government gave the state its approval to a first-in-the-nation program that will require everyone 18 and older to carry health insurance. The state’s universal health insurance program will use a combination of subsidies and penalties to make coverage more affordable and to encourage people to buy it.

Romney officials used the news conference to press lawmakers to close what they called a “loophole” in the law that fails to require all children have health insurance.

Health and Human Services Secretary Tim Murphy said as many as 40,000 children might fall through the holes, but lawmakers said they have already taken steps to expand coverage for children.