Twins are 4.5 years. Need new beds, that aren't too large to maximize the space in bedroom. I'm loving the look of IKEA busunge ( we have the wardrobe already and I do love to match) but I wondered what the lifespan of these beds would be, as in would the twins have outgrown them by age 8,9 for instance? Don't want to be having to buy new beds within 5 years!