My CC friend was on a BA flight last week, 53 passengers were staff alone with family, I bet there was a real scrabble for the best seats.
I don't know any crew that travel anything below Club personally, most travel 1st when the children are not with them but when they hit the age of 12 the whole family gets to go 1st.
This should be classed as a benefit in kind and taxed, just like any other employee receiving a perk! This virtually free travel to me is a huge perk.