I think it's far more toxic and negative to spoil and ruin a child. You're ruining an entire human life. And that's psychological abuse. The only people who find it amusing and cute when children behave badly in the most inappropriate of moments, are badly behaved parents...
I don't believe that you think that's happening here, I think you just want to put the boot in on Kate, and if you do think it then I would suggest that your authoritarian approach and ridiculously high expectations of small, tired children are extremely toxic in themselves. Kate wasn't finding it "amusing and cute", she was stressed, you could see that by how she nervously pushed her hair behind her ears.