That's how it was in the US until fairly recently. It changed in the last decade or two. I'm not sure why. Crime hasn't gotten any worse, as far as I know.
Say you have 10 parents that let their kids play outside. No one has a problem with this until an 11th parent shows up and it mortified, think the kids will all get hurt if they are allowed to be outside like this.
That parent makes a stink, take it to the city council, and a rule is put in place that you can't let your kids go outside without supervision. The folks making the rules think to themselves "well we had to act, there was such an outcry". Meanwhile the outcry is really just the outsized screams of one parent, and you've just screwed the other 10 parents.
I think it's related to trauma fetishization combined with child worship.
Trauma fetishization: The person who is most traumatized by a thing should be the one who dictates policy about that thing. People who have lost children qualify, and we literally name the laws after their dead children.
Child worship: Children are without trauma, and therefore without neurosis. When you traumatize them or through inaction allow them to be traumatized, you have created neurosis, which is the source of all problems in society.
My internal response: Okay? You're asking everyone to change a good-faith saying because it triggered a bad memory for you? Get over it.
Then of course once the rules change they will pump up how ridiculous they are.
People think they can win, but they are really just fueling the media.
It was a comedy music video about council workers (I wish it was still on YouTube, unfortunately I didn’t log into the account for a few years, and the channel seems to have been automatically terminated and I couldn’t find any way to restore it). The current affairs show had obviously tried to create some controversy that workers might be offended, and they interviewed a bunch, literally asking multiple questions to try and get them to say something negative, but they all loved it and thought it was funny. They even got an interview with the mayor and he liked it.
But they were still pushing the line. The piece ended with “but at least this time, no one was offended”. It was hilarious just the extent they were trying to manufacture controversy and drama from literally nothing, and how much they failed but still tried to push it! It was so bizarre, absolutely nothing about our song was mean spirited!
Don't take this for granted. I suspect this behavior is actually caused by an inherent anxiety in some subset of the population. When they don't have real (and likely) dangers to worry about, they will find some kind of tiny risk and overamplify it as something to focus their anxiety on.
Removing all things dangerous from the environment will only serve to amplify their tendency to do so. A mum in a high risk high crime neighbourhood is probably more likely to let her kids roam free (and less worried) than mums in upper-middle-class neighbourhoods where there is virtually zero crime.
My hypothesis is that the solution is to let children experience activities that are moderately dangerous (ideally through risk of pain, minor injury or some social stress, with risk of death or permanent injury kept minimal). This helps (I think) callibrate their ability to estimate risk as they grow up.
This would allow them to ignore imaginary risks like the one discussed here, and may help them identify situations that come with real danger.
Sometimes it even gets just a little annoying - how come my youngest sibling gets to do things at a much younger age then I was allowed to? :)
You're right, in that it's not that you care any less about your later kids, but you tend to be more pragmatic about child rearing. Better at recognizing the important events and problems, while shrugging off and ignoring the trivial stuff. You learn that you don't need to worry about a kid eating a crayon, and you recognize that certain pain cries mean "I'm not really hurt." You realize that sometimes the best thing you can do for a kid is ignore them and let them figure stuff out themselves.
Its quite possible that increased organized sports and after school activities (particularly robotics, math, computer science) could actually improve the capabilities of society as compared to just leaving the kids unattended after school.