Why did Mrs. Weasley say that?

[morsethanatos at yahoo.com]

No: HPFGUIDX 22445

I was reading Sorcerer's Stone over and I like began to seem very 
strange to me:
'"Now what's the platform number?" said the boys' mother.'(Chapter 
six pg 92 of the Scholastic paperback)

This seems extremely peculiar. Would she not know what the station 
was and where to go? Or is there actually another magic platform?