It appears that a sizeable number of Hogwarts students must be using King's Cross. So wizards are always traveling to and from the platform 9 3/4 at the start and end of the term of Hogwarts:
Harry's mouth went rather dry. What on earth was he going to do? He was starting to attract a lot of funny looks, because of Hedwig.
Also, the Weasleys are described:
The speaker was a plump woman who was talking to four boys, all with flaming red hair. Each of them was pushing a trunk like Harry's in front of him -- and they had an owl.
So how is it possible that no muggle ever notices the people 'disappearing' through the wall?
What's the probability that no one wonders about this 'weird' looking lot, with their trunks, owls, other pets, broom stick and where they disappear to?