Four Romanian men have been arrested in Berlin for the forced prostitution of minors, including their own children, police said Wednesday.

The four men aged between 26 and 55 are accused of bringing children and teenagers to Berlin, where the victims were forced to prostitute themselves in Tiergarten Park and Schöneberg's "Rainbow District."

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The fathers even prostituted out some of their own children to make money, police said.

The men were arrested in December in the Romanian town of Craiova in cooperation with local law enforcement following an investigation by Berlin state prosecutors and the department of organized crime.

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Police said they were members of a "family-related and organized network" of criminals.

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The children and adolescents have been taken into the care of welfare agencies in order to separate them from their families.

Berlin's Tiergarten Park has become a notorious drug haven and a place for men seeking to pay for sex with young boys.

Many of the young boys forced into prostitution are homeless refugees or from poor EU countries such as Romania and Bulgaria, according to the Berlin aid group Subway.