Invisible Family

Alright, listen up, Overwatch_Gamer321, you probably play a lot of video games, huh? Because you missed a pretty obvious one here. The joke plays on the word 'invisible' and how you can't 'look' at an invisible person. So, when the joke says the kids were 'nothing to look at,' it means you literally can't see them since they're invisible. It's like saying they don't exist visually.