Mohammed Alzamili and his wife, Hayfaa Yousif, came to Portland from Iraq in 2013 with three children in tow.

On Friday, six months after Alzamili and Yousif became U.S. citizens, their children became citizens, too, at a special ceremony held at the Children’s Museum & Theatre of Maine. They joined their younger sister, Layan, who was born here four years ago.

“I’m really happy. Now, all of my children are citizens,” said Alzamili, 45, who works for a delivery company.

Alzamili’s eldest, Abdullah, 13, served as his father’s translator and shared his sentiment.

“It’s a really happy day,” said Abdullah, still holding one of the small American flags that were handed out before the ceremony.

Abdullah was among 29 children, ages 1 to 17, who swore an Oath of Allegiance before receiving certificates of citizenship at the activity-oriented museum in Portland.

U.S. Citizenship and Immigration Services holds these special ceremonies periodically to recognize and celebrate the naturalization of children who have derived citizenship through their naturalized parents or through adoption.

About 1,000 Maine residents become naturalized citizens each year, according to the U.S. Department of Homeland Security.

Cindy Lembarra, director of the immigration services field office in Portland, spoke with warmth and clarity to the children lined up at the front of the small auditorium.

“An oath is a promise. Are you ready to make that promise?” Lembarra asked. “It’s a perfect day to welcome you into the American family.”

In addition to Iraq, the new citizens come from Burundi, Canada, People’s Republic of China, Democratic Republic of Congo, Ethiopia, Kenya, Sudan and Turkey. They reside in Biddeford, Kennebunk, Lewiston, Ogunquit, Portland, Saco and Westbrook.

Under federal immigration law, children who are under age 18 and were born outside of the United States automatically become U.S. citizens when at least one parent, including an adoptive parent, is a U.S. citizen by birth or through naturalization.

They also must be lawful permanent residents and be in the legal, physical custody of parents who are U.S. citizens, according to the federal agency’s website. If children meet those criteria, then their parents can apply for a certificate of citizenship, which allows them to apply for a passport, among other purposes.

Jocelyne Peace watched proudly as her three oldest children, ages 10 to 16, swore allegiance to the United States.

Peace came from war-torn Burundi in central Africa to Portland in 2011. Now, she works for the U.S. Postal Service, running a mail-sorting machine. Her husband is a maintenance worker, she said.

Peace’s children and the other young people at Friday’s ceremony swore to renounce allegiance to any foreign leader or state; to support and defend the U.S. Constitution; and to bear arms for the United States when required by law, among other things.

Now, all five of Peace’s children, including two born here in the last six years, are U.S. citizens.

“It’s a big thing,” Peace said. “It’s impressive for us.”