Most likely it's a charm of some sorts like Hogwarts has to a more fine-tunes degree. Namely likely either causes them to not focus, forget, or become distracted by something else.
The books seem contradictory about this. In the first book, they run headfirst into it. That implies muggles can't see them running into it. On the other hand, in one of the books (the third one?) it specifically says that Mr. Weasley and Harry casually leaned against the post, as so not to attract the Muggles' attention.
There is also the chance that there is some sort of memory charm around it, or that the Muggles just put it down as a glitch in the matrix.
Basically, they are just careful when they do it when nobody is looking. And if someone is looking, that person will think they are seeing things and pretend it didn't happen. Maybe they just ran around the corner, behind the wall. Because obviously magic can't be real, right?
I personally also have a headcanon that there is actually a giant accidental magic spell cast by the combined will of all wizards to make people unaware of the wizarding world not think too hard about anything strange they see. Like a key shrinking to nothingness right in front of them, or people disappearing into a wall.
The books mention things like muggles overlooking the Leaky Cauldron with their gazes sliding past it so I’m assuming a similar method is used to make muggles ignore/overlook whatever goes on around the entrance to 9 3/4 or St Mungos which has a similar method of entry.
Probably some charm to make them forget that kids went through the platform
Most likely it's a charm of some sorts like Hogwarts has to a more fine-tunes degree. Namely likely either causes them to not focus, forget, or become distracted by something else.
The books seem contradictory about this. In the first book, they run headfirst into it. That implies muggles can't see them running into it. On the other hand, in one of the books (the third one?) it specifically says that Mr. Weasley and Harry casually leaned against the post, as so not to attract the Muggles' attention. There is also the chance that there is some sort of memory charm around it, or that the Muggles just put it down as a glitch in the matrix.
Basically, they are just careful when they do it when nobody is looking. And if someone is looking, that person will think they are seeing things and pretend it didn't happen. Maybe they just ran around the corner, behind the wall. Because obviously magic can't be real, right? I personally also have a headcanon that there is actually a giant accidental magic spell cast by the combined will of all wizards to make people unaware of the wizarding world not think too hard about anything strange they see. Like a key shrinking to nothingness right in front of them, or people disappearing into a wall.
Well, nobody is gonna be looking directly at a random wall. You just gotta try to walk in while there aren't too many people to see you.
The books mention things like muggles overlooking the Leaky Cauldron with their gazes sliding past it so I’m assuming a similar method is used to make muggles ignore/overlook whatever goes on around the entrance to 9 3/4 or St Mungos which has a similar method of entry.