Our girls were similar in age (4 and 6) when we stayed at BLT. We are currently planning on a stay at BC next year when our girls will be 11 and 9. We have gone to WDW three times, most recently last year.
I couldn’t imagine our girls would have had as good a time at BC when we stayed at BLT. We probably spent 75-80% of our time at MK. I’m looking forward to our stay at the BC but Epcot is BIG! Even at this last stay our girls were practically wilting away toward the end of our days at Epcot. And there really wasn’t much for them there whereas the MK has a ton. I am hoping that now that they are older they’ll appreciate Epcot and the World Showcase a little bit more. Also they are much better swimmers and will enjoy SAB even more.
To me the biggest advantage that BLT has is the proximity to the MK. It was nice to walk or take the monorail if we so chose. And having the Contemporary as the first stop on the way back was more relaxing. Also it’s only one stop to the TTC. It just made things a little more manageable for us.