After throwing pointed barbs about each other for 90 minutes - about anti-Muslim rhetoric, sexual assault, supreme court justices and Syrian refugees - the presidential candidates were asked to say something positive about each other.
Hillary Clinton laughed and made the first reply without hesitation.
"I respect his children, they are incredibly honourable and devoted," she said.
"I don't agree with everything he says but as a mother and grandmother that is very important to me," she added.
Mr Trump retorted that he was "incredibly proud" of his children - his eldest daughter, Ivanka, and his two eldest sons, Donald Jr and Eric, were in the audience - but he said he was not sure whether Ms Clinton meant the remark as a compliment.
"She doesn't quit. She goesn't give up. I respect that," he said about his rival. "I'm a straight shooter. I say it like it is."
"I disagree with much of what she is fighting for," he added.
"But I consider that to be a very good trait."
The positive note at the end of the second presidential debate in St Louis might have been a relief for the candidates after an hour and a half of questions from the audience.
Mr Trump had accused Ms Clinton's husband, former president Bill Clinton, of raping a 12-year-old and sexually assaulting other women.
He also attacked her about the misuse of her personal email server, about her failure to abolish carried interest tax and Benghazi.
Ms Clinton said "so much of what he said [was] not right".
The Democrat focused on her opponent's anti-immigrant rhetoric, his negative attitude towards women and his taking advantage of tax loopholes.
