The TV host explained to Andrew that she wanted to hear from his father, but instead the four-year-old said, "I farted on you."
Lisa burst into a fit of laughter while Andrew's parents appeared to be embarrassed.
After the segment concluded, Tommy Little asked Lisa if it was the first time a person had farted during a news story.
"It's not the first time I've been farted on by a boy, that's for sure," she replied with a chuckle.
"I have two sons of my own."
According to the Daily Mail, Lisa shares sons Jake and Louis FitzSimons with her husband of 27 years, Peter FitzSimons.
The couple also has a daughter called Billi.
This isn’t the first time Lisa and Tommy have shared a laugh over explicit topics on air.
Earlier this year, Little revealed he had taken part in a naked bike ride!
The Aussie comedian admitted it had been a humbling experience after a passerby remarked on the size of his manhood.
"How's this for shattering? I was still quite cold but I thought, bugger it, I will get nude. Then, one woman, she was heckling from the side, yelled - 'He's a grower, not a shower!'" Little said.
An uncomfortable Lisa replied: "I'm not quite sure what that means."
"I think it means I've got a small c**k, Lis," stunning Lisa and the Sydney studio into silence in the final seconds of The Sunday Project.
Red faced, the Network Ten presenter buried her head in her hands and declared: "I'm done."