I think when it comes to "watching children", there are extremes, but the vast majority of us probably fall somewhere in the middle. And the middle is probably pretty large with room for lots of variation.
The personalities of the children also need to be taken into account. I remember a girl I worked with before I had children myself saying that her toddler daughter would sit in the back yard for a half an hour digging in the dirt with a spoon! I'd hoped for something like that when I had my own kids, but alas, God gave me two very active twins that kept me on my toes every moment. The first time I let them out of their stroller to walk in the mall, one ran one way, into a store and under a rack of clothes, while the other ran down an opposite hallway toward the door to outside.
I had to make a split-second decision so I ran after the one headed for the door, temporarily leaving the one in the store and hoping she wouldn't run further away.
At home I also remember them being missing and running around looking for them after my going to the bathroom or something. Couldn't find them until I heard laughter outside - despite the bitter cold and I think a dusting of snow, they were out on the swing set naked having a heck of a time. I wasn't one to hover, but I did need to use the eyes in the back of my head when my two were little because their personalities were such that they were each very active. A friend of mine who used to watch my kids for me sometimes, who had children two or three years apart herself, noted that (let's see if I can say this right)... with twins, they are both around the same intellectual level and you can't generally ask one to help with the other one or go do something the way you can with an older and a younger child. I had never thought about it that way, but it may help account for some of the craziness you feel with two or more the same age.
One of the problems for me, also (so I understand where LSUMiss is coming from) is that I spent three years working in a pediatric ER and saw things that nobody ever wants to see - a foot in a potato salad container that had been severed by a lawnmower, a drowned 3yo, lots of severe lacerations, abuse cases, burns from hot liquids, car accidents and hit by car, critical illnesses, etc. These aren't things you can just remove from your consciousness when you have kids yourself. All these years later I
still remember details - parents' faces, screams, sorrow. Safety was always a pretty high priority for me. At home we have a multi-level house but it was pretty safe as we had lots of gates and child proofing, until they learned to climb over gates or otherwise move to a different area. Outside our yard was fenced, and I had certain ways of getting the kids into and out of the car so one didn't run off into traffic (as I'd seen in one particular tragedy from the ER). Pools and the beach were probably the place I was least comfortable because even if other people were around, it was practically impossible to keep an eye on both children at all times (so in those situations, they generally wore vests). That period only lasted for a relatively short while, overall, until they were reliable not to run away and/or could swim on their own.
I think a pp, @firefly_irs, got it right when he or she said we're all doing our best.
Seemed to be fave thing to hide. Finally I made about 10 sets of keys and I played the hiding game
--which I know you're not doing just giving it as an example).
