The demonstration was organized by the ARCI cultural association, which has called the move "an act of discrimination and of persecution." The group encouraged participants to give their own fingerprints in a petition called the "imprint of racism."
Maroni said children would be fingerprinted "to prevent phenomena such as begging."
European Union lawmakers condemned the move, calling instead for an EU-wide policy that would help integrate Roma into mainstream society.
EU Social Affairs Commissioner Vladimir Spidla, the bloc's top antidiscrimination official, told parliamentarians that fingerprinting members of one ethnic group is "not acceptable" under EU law.