I go there quite often because my company's head office is there. Unfortunately I never have enough time to enjoy everything that Montreal has to offer. Last time I was there, I got to walk around China town a bit. It's not huge, but very cute. There is a guy there that sells Dragon's Beard candy from a little window shop, it's so good! I like going to Mike's on St. Catherines for breakfast.
I usually get deals on hotels through travel zoo or
http://www.tourisme-montreal.org/.
Here is a good website that lists stuff you can do with kids:
http://www.where.ca/blog/kid-stuff/50-things-to-do-with-kids-in-montreal/