Playroom with red carpeting and wood block window shade

Kids' rooms often tread transitionary territory when it comes to modern design. What might be good for a five-month-old may not work well to when he or she is five years old.

From the leafy sidewalk outside Paul Bernier and Joëlle Thibault’s home in the Plateau Mont-Royal neighborhood of Montreal, there’s no clue that their brick home is all that…