Of my regular visitors, only Wacky Hermit has small children, to my knowledge, though maybe Jerubaal does as well.
I try to offer some word of encouragement whenever I see a parent with children out in public, especially if anyone is looking ragged emotionally. This has to be done with some timing and delicacy, of course, so that it doesn't look like I'm trying to abscond with the kids. "Don't make your mother crazy. It doesn't work. Trust me on this." is a common line of mine. It cautions the child lightly and humorously, and is also meant to both comfort and caution mother. Yes, they are being difficult. You are in a stressful situation. You're not looking crazy yet, but it could happen.
Yesterday a boy of about four was leaving the supermarket with his mother and slightly older brother. The younger boy was looking at his perfectly unremarkable index finger and crying. It was a ratcheting up cry, which bid fair to turn into a melt-down scream soon. As in seconds. Mother was carrying bags and striding toward the car, talking him down with sweet, encouraging, but very weary words, like a rehearsed litany of comfort talk. A comment from a stranger can sometimes stop a crier in his tracks, the sudden change and uncertainty taking him out of his little self-focussed world just long enough to forget what he was crying about. "Your finger looks okay, lad" I said. Mom smiled "D'you want him?" "Oh, he's going cheap at the moment, is he?" "Very cheap." I got to use one of my other standard lines for these occasions. "I've had four. They don't graduate from highschool like this."
I honestly don't know why people tell parents with small children that these are wonderful ages and the best times, and that it's much worse when they're teenagers. Do they want to make these young couples suicidal? It's much, much harder when they're young. Yes, teenagers can get into worse miseries of drugs, crime, stupid driving, stupid sex, and a dozen other things that could ruin their lives, and worrying about that is stressful. But they aren't doing these things every minute of the day, requiring your attention. And they can go to the bathroom by themselves, so that you don't have to spend your day applauding excrement. And they can make their own sandwiches.