It takes considerable effort to "allow yourself to sleep until you are "fully slept"" if you are woken up by a 2 year old sitting on your head and trying to get you to look at a book with him.
“Fully slept....” That’s the dream. My daughter will try to open up my eye lids whilst I’m asleep and then start yelling “it’s morning time” at the top of her lungs. She has done this before at 4am and now I jolt awake at the sound of her entering our bedroom. Sadly it has been very effective at waking me up, and it’s hard to train her out of it when it works so well. To be honest I think I’m also sort of hard impressed by the brutality of it all.
Having kids changes many things. Certainly, your opportunity to sleep fully will be hampered.
However, if the responsibilities are shared between multiple adults, you can still get it done some of the time, and be well-rested and comfortable for when it's your turn to watch the kids and let other adults do their sleeping.