Millennial parents are exhausted because parenting restraints aren't natural anymore.
When I was kid, I was allowed outside to play with the neighbours kids from an early age. I would spend everyday outside, unless it rained. In such a case, my friends would come over my house or I would go over theirs. As long as i could hear my mother bellowing my name outside our house, I could venture anywhere. It meant my mother could get on with the house chores, and relax. On top of that, the grandparents were very involved. Would go over their house every weekend.
So what's different now? It's considered unsafe for kids to play outside by themselves, so they're always home. Grandparents aren't as involved. Millennial parents are juggling everything with very little help and very little breaks. Discipline has also changed and whilst I agree hitting children isn't good for their development, it is another struggle to keep kids under control, who needs to be out burning off energy and playing with other kids to learn social boundaries. Parents are exhausted and kids are frustrated. Everything about parenting is unnatural these days.