(CNN) Baltimore became the largest city in the United States to bar soda and other sugary drinks from restaurants' kids' menus this week.

The Baltimore City Healthy Kids Meals Bill was signed by Mayor Catherine Pugh in April but went into effect Wednesday.

Restaurants will be limited to offering children's meals with flat, sparkling or flavored water with no added sweeteners; milk or non-dairy alternatives; or 100% fruit juice. Parents can choose to order other drinks for their children, however. Baltimore's health department will enforce the law through its inspection process, and those restaurantsfound violating it could face a $100 fine

"It's not a ban, because parents still have the option to choose something else," said Shawn McIntosh, executive director of Sugar Free Kids Maryland , a coalition that aims to prevent chronic illnesses in children and has worked to increase support around the policy with local lawmakers and the public. "They can ask for something else. It's just that the options that are listed on the menu are healthy options, so that what kids are confronted with are healthy options."

The health department will work with restaurants to help make the transition if they haven't already, said Dr. Leana Wen, Baltimore's health commissioner.

"Passing a law that creates healthy environments is within everyone's best interests, and so there are no drawbacks to having healthy options as the default option," McIntosh said. "What parent doesn't want their child to drink healthy for the most part? When I was a kid, drinking soda was a treat. You didn't drink it on a regular basis. And our hope is actually that parents start thinking about how it really should just be a treat and can be a treat when they want it to be a treat. Not something that is always in their face."

Not everyone is happy with the law, and detractors argue that it may affect a restaurant's bottom line.

"The Restaurant Association of Maryland opposed this legislation," Melvin R. Thompson, the organization's senior vice president of government affairs and public policy, said in a statement. "Public policy that interferes with the minutiae of restaurant operations exacerbates the business challenges already facing City restaurants.

"Some quick-service/limited-service restaurants may be forced to use single-servings of water, milk or juice for children's meals, which often cost more per serving than fountain drinks," Thompson added. "The increased cost could cause some restaurants to either increase the price of children's meals or sell beverages separately. Such a change in the bundled price, or selling beverages separately, may reflect negatively on restaurants if customers perceive a decrease in the value of children's meal pricing."

But proponents of the new rule say it will help curb the growing number of obese children in the city. One in three school-age children in Baltimore is either overweight or obese, and one in four drinks at least one soda a day, according to Baltimore's health department . Just one sugary beverage per day can raise a child's risk of becoming obese by 60%, a 2001 Harvard study found

"The number one killer of both men and women in Baltimore and around the country is heart disease," Wen said. "That's fueled by high blood pressure, diabetes and obesity. I'm an emergency physician, and it used to be that I treated only adults with these problems. Now, I'm treating children who are 8 years old and weigh over 200 pounds. I see teens as young as 13 years old who have high blood pressure and adult-onset diabetes."

Seven cities in California and the county of Santa Clara, as well as Lafayette, Colorado, have instituted similar regulations, according to Baltimore officials. The department coordinated and collaborated with them to learn from their experiences, Wen said.

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Other major cities like Philadelphia, Seattle and San Francisco have implemented additional taxes for sodas. A bill to place warning labels on sugary drinks in Baltimore failed two years ago.

"The bottom line about this legislation is that it is a win for public health," Wen said. "This is something that parents -- together with community members, with public health officials, with doctors, with pediatricians -- this is something that we have championed that's for the best interest and the public health of our children. And we're very glad that it's passed. And we know that this is something that will have impact for our children and for generations to come."