Hi Leah. Sorry that I just read your dream now as I've been away from the forums.
Wow, interesting dream. Not too hard to interpret though! Your dreams often mirror what is going on in your waking life only just in symbols.
Previously the building in your dream has been "under construction" because your waking life career has been a work-in-progress as you built it.
Seems as though your family now lives in this same building, perhaps because there is major crossover with your family life and your career (is a home-based office, for example?)
But underneath the work/career focus lies an amazing, enriching place you've created for your family. Usually, the underground floor represents the subconscious but in this case, it is more like foundation of this building.
You have established a very positive foundation for your family. You seem more sure, confident and creative. You wished that when your kids were younger, you had felt this way and could have offered them more of this type of experience and understanding earlier.
Hope this helps. Great dream!