I'd say it's about a 5-8 minute walk without kiddies, perhaps a few minutes longer with kids, from the far side of the villas building. I was just saying on another thread that it appears to me that many of the YC rooms would be a longer walk to SAB than from BCV.
We stayed in room 559 (a studio) at BCV in Sept. It was very convenient to the quiet pool but a bit longer to the main part of BC. It didn't bother us at all (it was very quiet and we had a great view of Epcot!), but you might like to be closer to everything for your kids.
The great thing about BCV is that nothing is too far away, unlike at some of the other DVC properties. We stayed at BWV last year, and it could be quite a hike to get places if you weren't at least somewhat near an elevator. I find BCV much more manageable -- and preferable for people with little kids.
Have a great trip,
Sarah