Funny enough I know lots of millennials without children with horrible sleep patterns and habits.

But you might be up to something: people are too stressed/anxious/depressed (without children) that adding children seems to them like an impossible burden. Now, I am not sure children would not sometimes actually improve their state (biology kicking in), but definitely is a gamble.

Children surely help you get your shit together. Otoh if you don't have your shit together, adding children into the mix is a little unfair to the children.