Namey yep I see the logic - but you don't have 5 spare bedrooms, you have 2 "spare" bedrooms not used as bedrooms but set up as a playroom and a study.
5 spare bedrooms though - just why? Why buy such a ridiculously large house for such a comparatively small family? Obviously people can buy whatever house they want, but I'm curious. Are these rooms like Monica's shiny guest room, all set up with nothing to do? Or are they in fact "spare" in inverted commas because the parents have a study each, one is a "den" with a TV and games consoles, one is a hobby room, one a guest room... But if you have 7 bedrooms the downstairs must also be very large for just 4 people, two of whom are very small to rattle about it, with space for those things downstairs, so it seems unlikely...
Even if I had untold billions, I wouldn't buy a house with 5 rooms which would be left empty to rattle about in. I want to know why anyone would want that :o
When I was a child we had friends who lived in an old manor house. They must have had at least 20 "spare" rooms, but you had to wear your wellies to go into them and some were cordoned off with builders tape - only the kitchen and living room downstairs and a couple of bedrooms were habitable and none of the house had central heating. The bathroom was fascinating because there was a row of wooden toilet seats all joined along one long bank, meaning lots of people could go to the toilet at once in one room... 
It was great fun to play hide and seek in (though looking back it's probably a miracle none of us were ever injured falling through a floor/ ceiling or on rusty nails etc) but I often wonder since what on earth their parents were thinking!
Presumably Matilda 's house is in a good state of repair though, I'm just wondering why she'd want multiple empty rooms.