My vote would be to get the free rollers from leelau, and pick up a cheap magnetic windtrainer as well (I think MEC sells them for a good price). I'm sure the fluid windtrainers are quieter but they are higher priced and I have heard they don't last as long. The windtrainer seems to be to be safer compared to the rollers if you have the kids around you at any time.
I hear what the others are saying about the benefits of going riding no-matter the conditions, but with a young family you have other things going on as well. The rollers/wind trainers allow you to get in some exercise after the wee ones have gone to bed.
The problem I found with the indoor training though is that it can get boring very quickly! I have only been using the windtrainer for a month, but to keep things interesting I bought a playstation2 so I could spin in front of the TV and play games like offroad fury and downhill domination. As an added bonus the kids enjoyed watching and attempting to play the games as well.
Another interesting option that I recently saw at the LBS was the indoor spin training DVD's. The DVD's lead you on a ride through different road oriented terrain, and coaches talk you through intervals to make the workout more intense and efficient.
Sorry for the long post but it's something I had been recently putting a lot of thought into.