As she prepared breakfast for the boys and for Luke's twin sister, Jillian, on Oct. 22, Sara Johnson heard their voices coming from the playroom.
"I first heard Wesley, the oldest, saying, 'I'm Mitt Romney, and I'm going to take your job, President Obama,'" she recalled in an interview with ABCNews.com Monday.
Intrigued, Johnson, of Midlothian, Va., grabbed her iPad and started recording her sons' conversation - which got even more interesting.
In a video, which she uploaded to YouTube, the two boys can be seen sitting across from each other at a table. Both boys are playing with building blocks as their sister stands to the side, silent.
Wesley, dressed in a dark-blue T-shirt, says: "I'm Mitt Romney."
His brother, dressed in a red T-shirt, replies: "I'm, too."
Wesley objects. "No, no, no! You're President Obama, so you didn't win."
Now Luke objects. "I win!" he said.
Each boy is raising his voice even louder, each now slamming his building blocks onto the table as if to emphasize his point.
When Luke tells Wesley that he (Obama) wins, that's the final straw. Wesley throws a building block across the table, hitting his brother in the forehead. Luke cries.
Wesley got into trouble immediately for hitting his brother, Johnson said, but she was mystified as to how the boys knew about the campaign.
"I've never talked to the kids at all about politics, the election, they don't watch a whole lot of TV, but when they do it's always one of the kids' channels … and in the car, we don't listen to the radio. They watch DVDs all the time, so I was just baffled to hear," she said.
Added to that, Johnson, 30, is an Obama supporter.
"So for him to be talking about Mitt Romney stuff too, I was just like, 'Wow, where are you getting this?'" she said, laughing.
When she asked her boys about it, they told her that their preschool teacher had mentioned the election in class.
The YouTube video had been viewed more than 54,000 times as of Monday night.
Some online commenters have mentioned that Wesley was mean to his brother.
"They don't know us," Johnson said of the commenters, adding of her sons: "They're 4 and 3, and they have no clue what they're talking about. I just think it's funny. My kids are awesome. They're sweet, and they have good intentions."
"This happens multiple times a day," she said of the boys' disagreements, adding that she's used to it.
"They're being nice right now, but they were just beating each other up again. … It could have been anything. It could have been a Batman and Spider Man conversation, or Angry Birds or something you know? It could have been the same conversation just with different characters," she said.