All a bit hypothetical at the minute but a house round the corner I really like is probably going back on the market soon and we are having another baby (DS1 is 7, DS2 is 5) and will need to move at some point.....
House is a bit odd in some ways,has good parking and nice garden although not great light. It has lounge, dining room, kitchen and one other room downstairs that we would probably use as a bedroom, upstairs has main bedroom with big en-suite, large 2nd bedroom and a decent sized shower room. So we would need to do a bit of work and probably chop the 2nd bedroom in 2, to make 2 kids rooms approx 10 foot by 8 foot. But, there is a fairly substantial outbuilding which I think could be turned into some sort of kids den.
The alternative would be to look at moving a little further into nearby area with big old terraces where we could probably get 4 decent sized bedrooms, but with less living area, less outdoor space and no outbuildings/garages etc etc.
What would you say is more important, size of kids rooms, or other space they can hang out? We need this to be a house we will live in a for a long time but I'm finding it hard to imagine life with a 7 year old, a 12 year old and a nearly 15 year old 
(Also DS1 has ASD - he needs his own space but is unlikely to be the sort of teenager who has loads of friends round all the time. Unless he finds a group of nice geeks with a similar compulsion to study train maps....)