Lizzie knew something was wrong when her child of barely a year in age showed more self control and maturity than his father. Davey screamed bloody murder. Threw things. Threaten violence against anybody near whenever he felt like it. Which was more and more often.
At first Lizzie ignored his inordinate behavior treating him like a schoolboy fishing for attention. He'd have to learn the universe wasn't his alone. It was funny the way Frankie did listen when told to calm down, he ended temper tantrums rather quickly. She couldn't understand why Davey couldn't. It's when he started threatening that violence towards Frankie did the fear arise.