spend their free time (otherwise spent watching tv/movies/sports, golfing, fishing, etc) at work instead.
Perhaps it means getting up an getting in the office earlier or working from home after everyone has gone to bed.
There is a balance needed and balancing how to spend your time is one of life's great challenges.
For me - I chose to spend more time working when my kids were 3 years old (and before they were born) so that I could spend more time with them when they were 8.