Are Down's Syndrome people happier than other people?

When I see little Down’s Syndrome kids at the store they are always so sweet, smiling and sometimes reach out to touch me. A woman up the street dances on the sidewalk while she talks to her dog. Is it my imagination or do these victims feel joy from not knowing what’s going on? Or do you know someone who is depressed who has the disease? Does “ignorance is bliss” apply here?