Would I have sex in front of my children? No, I'd be too embarrassed.
Do I think that couple did anything to psychologically endanger their daughter? No. I think that sex should be taught in a loving environment. The daughter is probably going to see intercourse in a porn movie (or TFP Exhibition Forums
) anyway, but won't see it done properly.
I guess if the daughter was not forced or overly-encouraged to watch, I say no crime was committed.