> most of my chance interactions lately come from talking to other parents while my kids play in the street or playground.
I think there's a signal here that's the difference. If I'm on a bus, I probably don't want to talk to anyone. Similarly, if I'm in a grocery store, I don't want to talk to someone in the baking aisle, I just want sugar. But if I'm out with my kid/dog, I know that's an inherently more sociable situation that may end in an interaction.
> Sure, usually it's a pleasant hello and then not much, but sometimes you meet people you get on with really well.
I've a dog and live in Edinburgh, I've found that the people I get on with are people I see repeatedly. Neither of us made the effort the first time, but after 2 weeks of seeing each other every morning at 8:30 in the rain and the dogs saying hello to each other, you can end up talking. I immediately have more in common with this person than going to the same destination as them, for example!
Funny enough I was at a playground a few weeks ago and my kids envied another kid's sled, they talked and the other kid was happy to share, and I talked to the dad who had also moved here from Ireland and even had similar interests (Green party member, etc.). Sure, usually it's a pleasant hello and then not much, but sometimes you meet people you get on with really well. I don't think that would have happened if I had just been sitting on the bench looking at my phone while my kids played.