For the first year they are so helpless they literally can't fall asleep without you (unless you let them cry for hours). You basically have to keep an eye on them every waking moment if they're not in some kind of enclosure. Even simple things like taking a shower, let alone going to the store are logistical problems.
I have no idea how single parents do it
True. If you got two kids (I do) one can just look for both while the other one can have their shower/toilet/sleep whatever. Actually we are often taking turns sleeping.
Even larger communities. I don't think nuclear family is actual the natural state for our species. But recent invention.
Things start to scale much better once you get to bigger family units, with 3 or even 4 generations present. Grandparents, uncles, sisters and brothers of different ages. Looking after the kids. Or in tribal society whole tribe up to 100 people.
