A 68-year-old Russian doctor was convicted on Tuesday and sentenced to five and a half years in prison on accusations that she told a young boy during a medical appointment that his father, who was killed while fighting in Ukraine, deserved to die.

The conviction of the Moscow pediatrician, Nadezhda Buyanova, reported by the Tass state news agency, is one of a flurry of criminal cases punishing ordinary Russians for voicing opposition to the war. But it is unusual because it relied in part on the testimony of a 7-year-old boy, whose mother originally said he was not in the room to hear the doctor’s comments but then changed her account a month later and allowed her son to be interviewed for the case.

Ms. Buyanova was charged with “disseminating false information” about Russia’s military campaign in Ukraine. She denied the accusation in court, saying that she did not discuss the war with the boy.

The court did not allow the boy to be questioned during the trial; instead, prosecutors submitted minutes of a pretrial interview. A lawyer for Ms. Buyanova questioned the veracity of the statement, saying that the notes read like a prepared narrative with words and syntax too complex for a 7-year old.

“Those phrases like ‘legitimate target’ and ‘aggression’ — I very much doubt that a young child can say that, let alone remember and repeat it,” the lawyer, Leonid Solovyev, said in an interview.

The case has provoked condemnation among rights groups and health care workers, more than 1,000 of whom signed an open letter posted on social media this year in support of Ms. Buyanova. The case, they said in the letter, sends a “strong signal to young people: Don’t enter the medical profession, don’t help people — they can always speak against you, and you will land in jail.”