Here's why:
* She doesn't remember their names. When Montag asks her about their children, she struggles to recall their names, even though she claims to love them.
* She prefers the company of her "family" on the parlor walls. Mildred finds solace and entertainment in the television "family" and doesn't seem to have any real interest in spending time with her own children.
* She doesn't seem to care about their well-being. When Montag mentions that their children were taken to the hospital, Mildred is indifferent. She doesn't even ask what happened or seem to care about their condition.
This detachment from her own children highlights Mildred's entrapment in the superficial and artificial world of the dystopian society. She's so consumed by technology and entertainment that she has lost the capacity for genuine human connection, including with her own children.