Hi CryptoDave - your post makes me realize how lucky I am. I introduced both my son and daughter to collecting and it stuck with my daughter. At 21 it's not on the top of her priorities, but we do get to spend some time together collecting from time to time. I've also let her know where to find the value in the collection should she ever want to sell it in the future.
I would recommend looking outside the family as an alternative. I've
inherited 2 collections from family friends in the past. In both cases there were no stamp collectors in the family. In addition, I believe both families were shocked how little the collections were worth. The material I received remains a valued part of my collection to this day.
Paul