Why are some kids so bad?

questioner1991
Today I was at work and the mom left her kids with me in the waiting room. In 12 minutes they literally made a huge mess in the restroom, ran everywhere, knocked down the shelves, changed all the thermostates called me a poo face lol, were screaming and just so bad. Where I work it is an area for people to relax and they were just so bad I am sure the clients had a hard time relaxing. How could a kid be so bad? and should a parent leave their kid at home and not bring their kid to a supposed to be relaxed setting and have a stranger watch her kids who are so misbehaved? I never really grew around kids. I am curious, do you think this is the parenting style or just the kids temperment?
Why are some kids so bad?
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