TV, The Cosy's, and Children

I am still trying to decipher what is happening on my favorite Chinese comedy. So it is a family comedy...which makes the vocabulary a little more understandable. Think Cosby Show - everyday household situations that they make hilarious.

So China has this one child policy, which in the cities, I hear is strictly enforced to keep the population from exploding more.

How come on this TV show, there are two sons in the house? When I first started watching it, I thought that there were really 3 kids because a little girl was always in the house too. But it turns out that her character is more like the character Kenny (aka Bud), Rudy's friend who was always at the house and seemed to eat most of his meals with the Cosby's.