this was not really an issue before food delivery apps came into fashion

btw. kids up until certain age can pretty much in all countries ride bike legally on sidewalk, are there any countries where 8yo can't ride bike on sidewalk?

It's a problem in the US where bicycle food delivery is really rare. Even in places with good bike lanes, they'll often prefer the sidewalk because if there is some sort of obstacle in the bike lane (e.g. a car that parked illegally), it won't jump out of the way for them like a pedestrian with a sense of self-preservation, which would mean they might have to slow down.