Potty-mouthed parents, ill-behaved kids. Big surprise.
I see no reason to believe that anybody who uses words like those on that site necessarily use them in front of their children. There are circumstances where swearing is appropriate.
A Soviet joke will, perhaps, illustrate my point:
In a kindergarten, the teachers discover that all the children have started swearing terribly. An investigation begins, and soon it turns out that two electricians - Petrov and Sidorov - had visited the kindergarten in the morning to work on some fixtures.
They are questioned by the headmistress, and Sidorov explains:
"We are innocent, Comrade. You see, Petrov was soldering a fixture, and I was holding the ladder he was standing on. Suddenly, I feel great pain - and I exclaim:
Petrov my dear friend! Do you not notice that hot solder is dripping onto your good friend's neck?