Do you understand?

The last couple of days have made me question how much my daughters understand what is going on with their mother.  I know the oldest understands.  She has stepped up and really done a good job of taking care of her younger siblings.  Yesterday when we were gathering things to pack for my wife, the middle girl asked if her mommy was going back to the hospital.  Obviously, she remembers the last time this happened.  Today when I came home for a short time my youngest daughter asked where her mother was.  I reminded her that we took her mother to the hospital.  She said ok and returned to playing.  It makes me wonder, do my daughters really understand what is going on around them?