Don't you hate it when your dad starts building mud-and-garbage sculptures in the living room? Annoying, right?
For Neary's poor kids, the UFO phenomena and their father's erratic behavior are a bit too much for their young minds to deal with. To be fair, it would be a bit much for most adults to wrap their heads around.
Brad, the eldest, has the hardest time dealing with Roy's change from everyday father to obsessed fanatic. At first, he thinks of it as a game and claims to believe in the aliens. He even jokes with Toby that he's an alien, too: "You live on the moon. I saw it. You came through my window last night."
But as Ronnie becomes more distant from Roy, their marital stress begins to wear on Brad, who gets angry as his family structure breaks down. As a depressed Roy sits in the shower fully clothed, Brad slams the bathroom door repeatedly, shouting, "You crybaby!"
The younger two children, Toby and Silvia, remain pretty much unaware of the family breakdown. Both see their father's behavior as a game he's playing. Silvia plays with her potatoes, mirroring her father. When Roy goes bonkers and starts throwing bushes, bricks, and chicken wire into the kitchen, Toby helps him and asks, "Dad, after this can we throw dirt in my window?"
It's at this point that Ronnie gathers them into the car and drives them to her sister's house. In one of the film's weaker plot elements, this is the last we see of the children, and their stories remain unresolved.