The Brooklyn operation of the real estate firm Brown Harris Stevens is facing a lawsuit from a couple who says the firm would not allow them to rent certain apartments because they had a young child.

The lawsuit is a class action on behalf of any families with young children who Brown Harris Stevens Brooklyn LLC may have steered away from certain listings. But the civil complaint, filed yesterday in U.S. District Court in Brooklyn, is very much the unhappy story of one family’s search for an apartment.

Back in May 2006, a computer consultant named Jamie Katz and his visibly pregnant wife, a physician named Lisa Nocera, decided to leave Manhattan and move to Brooklyn, the complaint said. They were hopeful about an apartment they had seen on the real estate firm’s Web site: a unit in a converted carriage house on Hunts Lane in Brooklyn Heights. But an agent at Brown Harris Stevens, Aileen Truesdale, refused to show them the apartment when she learned Ms. Nocera was pregnant, according to the complaint. The couple was told that the apartment’s owner would not rent to a family with children, the complaint alleges.

The next year, another agent at Brown Harris Stevens told the couple that the owners of a Lincoln Place apartment in Park Slope would not rent to them because of the owners’ concerns about lead paint, given their now 1-year-old son, the complaint alleges. The real estate agent who showed that apartment, Miya Signor, seemed to sympathize with the couple : After Brown Harris Stevens declined to refund the $50 that the couple had put down for a credit check, she offered them a refund out of her own pocket, the complaint alleges.

At this point, in July 2007, Mr. Katz and Ms. Nocera turned back to Ms. Truesdale, the agent who would not show them the converted carriage house the year before, to express interest in a two-bedroom apartment on State Street in Brooklyn Heights that had huge windows, a garden, and a monthly rent of $3,000.

Once again, the couple was told that the owners were concerned about lead paint and the risk of renting to a couple with a small child, the complaint claims. Under New York City law, landlords are required to abate lead-paint apartments in most homes, a lawyer for the couple, Mariann Wang of Emery Celli Brinckerhoff & Abady LLP, said. It is also a violation of the federal Fair Housing Act to discriminate against families with children, the complaint alleges.

“All of the sudden, just because they had an adorable toddler, they were somehow pariahs,” Ms. Wang said.

The lawyer said she believed that landlords often voice concerns about lead paint as a pretext to avoid renting to couples with children. The complaint notes that, at the couple’s request, an investigator at the Fair Housing Justice Center went to the State Street apartment and spoke to some workmen who were painting the apartment.

Asked about the lead paint, one workman said: “If there’s lead in the paint, it’s like under at least 10 layers of paint.” A spokeswoman for Brown Harris Stevens, Melissa Hill, declined to comment on the suit. In the end the couple took another apartment in Manhattan, according to the complaint.