Oh wow I think we had these on the way to school when I was a kid too. Everyone told us not to eat them so we used to put the berries in our mouth and spit them out to show how tough we were. Wow we were very very stupid kids.
If they had told you they were highly poisonous instead of just telling you "not to eat them" you might have taken them more seriously. And if they had given you a taste of the red berry around it (which is sweet but not that special either, and the texture is not great) you might just have thought it was not necessary to play with them at all.
But that requires education at all levels, around here (Belgium) I sometimes see parents who seem deadly afraid of anything nature, I tell my kids to eat blackberries and they softly tell their kids next to us not to do that. You end up with generations who just don't know anything about what's around them and will eventually do stupid things.
Me to my 3.5-year-old boy after evening bath (winter here right now): Your feet are going to get cold, don't you want to put on your slippers to keep them warm?
Him: No!
And if I put them on he'll take them off as soon as I'm not stopping him from doing so.
For putting on warm enough jacket for school I try similar reasoning which has yet to work with any kind of consistency, still mostly lands up having a bit of a tantrum all the way until I hand him over to his teacher.
His two-year older sister was a lot less difficult at his age.
we will pick up that book about the monster, it is really scary (slippers on already) and we will sit on the sofa (already carrying the child). Are you cold? Let’s find that pink sweater…
Also, it works wonders to let them make a choice between two acceptable solutions instead of giving them space to say no.
"Do you want the slippers or the thick socks?"
It doesn't always work, but kids that age are learning to set boundaries, and giving them the illusion of agency often helps.
Sometimes the old-world spook stories work.
For that, parents would need time. But if we have to spend half of our day with work or work-related tasks (commute, lunch break)...
Society (or let's be real, capitalism) forces us to work unhealthy amounts of hours and then wonders why there aren't enough children and of the children that remain, they dumb down every year...