During the winter, it's hard to find activites to keep two active kiddos busy and entertained without going nuts (especially when the temps don't get above -10 for weeks at a time, it seems!), so I tend to look at different craft ideas as well as pulling out "special" toys that I've stashed during the year.
One really fun thing we discovered this year were "melty bead" -- also know as fuse beads. You take these little soft plastic beads and put them on these pokey boards in any shape you want (some boards are already in shapes), then put a piece of parchment paper (VERY important) over the beads before ironing them. The heat from the iron causes the beads to melt, or fuse, together, thus creating a fun project for kids (and grown ups) to do.
My kids, and especially Luke, have LOVED the melty beads activities. There is a company where you can also get larger sized beads for littler hands. They come with a book where you can put the pokey board over different pictures and put the large colored beads on the indicated spaces, making fire trucks, police cars, flowers, puppies, butterflies, and more.
I LOVE the melty beads because they're fun (and I have to remember not to hog the pokey boards from the kids!), they're great for kids to see what they can make, they can help you teach the kids color coordination, or you can just let them have at it and let their creative side run wild!
You can find the larger ones at http://www.klutz.com/ (I LOVE Klutz books!); the smaller (regular) sized beads can easily be found at craft stores and also Walmart...you can also do a quick search online and find lots of different places that have them available. Here is some of our work!