Sleep Cycles

Newborn: you wake them every few hours to nurse to make sure they grow strong and healthy.
Infant and Toddler: you do whatever you can to keep them from waking so they can be rested and not cranky.
Preschooler: you want them not to sleep so deeply that they don't wake up when they have to pee or else you end up waking them up in the middle of the night to preserve a dry bed.

And then you get pregnant and never sleep well again in your life because pregnant women don't sleep well and once you give birth, you become a mother who hears every little sound that goes bump in the night. Which is a good thing because you have to wake up to feed the baby and potty the big sister!