I'm not sure if this is an exclusively Canadian-American tradition or whether it was something that evolved as a polite game in the 1920s or 1930s throughout America, but all of my relatives on my mom's side used to get together for Christmas for a big gift-giving game.
Each person is asked beforehand to bring 3 or 4 low-cost wrapped gifts. Before the game starts, all the gifts are put in the center of the room in one or two large piles.
The game involves two decks of cards and a caller. The caller brings the first pile of gifts to a spot in the center of the room, and deals out all the cards to everyone in a circle. It's okay if some people get one card less than the others; what matters in the game is who has the caller's last called cards.
Once one deck is dealt out, the caller shuffles his own deck of cards, and starts drawing a card at a time. Whoever has a matching card from the first deck of cards gets to go up to the gift pile and take a gift back to his or her seat. If the gift pile is gone, then that person can steal someone else's gift! When the second deck is completely called through, everyone gets to open their gifts. If someone gets something that's really not his or her style, s/he can trade with someone else who wants it.
What makes this game fun are the wacky, odd-shaped and inexpensive gifts that get stolen over and over. One of the most swiped gifts from a past game turned out to be a wrapped roll of toilet paper with a can of tuna placed on top of it... the unique appearance made it such a conversation piece and we all got a big laugh out of seeing what made up the mystery shape.
I'm not sure how old your grandchildren are, but in the past mothers could play the game for their kids and give their kids the gifts they won. Sometimes it was priceless watching a mom send her kid toddling across the floor to steal a gift and come back with a great big smile.
Whether you can use this tradition or not, a very merry Christmas to you!