So you brought the kids, and grandma, to Ottawa - what are you going to do to keep everyone happy? HELLO?! What are you going to do first, is the question! There are so many places it can actually be a bit much to wrap your head around. My first recommendation is Parliament Hill.
If the kiddies are in school and have talked a bit about the country and government, you really have to take a guided tour of the Parliament Buildings. The gothic buildings are actually the second structure to stand on Parliament Hill and though not the "originals" they are absolutely gorgeous and the history is fascinating.
The first set of buildings was destroyed by fire, but the great library and all the historic documents were saved when a clever archivist closed the huge, heavy doors that separated the library from the centre block. You can also sit in on the sessions and watch the government at "work." Also feel free to wander around the grounds - they are beautifully landscaped and dotted with interesting historical statues.
July 1st is THE day to be on the hill. Why? Because it is Canada Day, the country's birthday (born 1876) and the one day a year when Ottawa goes completely crazy. Everyone from the downtown lawyers and politicians to the littlest preschooler is wearing something red and white or waving a maple leaf. Streets are closed to traffic around the hill for the concert and fireworks. Always an awesome showcase of Canadian musical talent, and the fireworks are traditionally put on by world-class professionals.
In Ottawa in winter? First of all, why? And secondly, don't despair, the weather may be frigid, but the welcome will be warm.