I think slang should be allowed. I mean, not all slangs are harm and as long the tv programs use it in a positive way, i think that's alright because we live in modern world, and not all of us speak formally. And for the babies, i think it depends on how their mother treat them like "oh, don't speak that words again"
Slang is part of the evolution of language and used in everyday life. However, I'd say that at least in some contexts proper speech should be insisted upon for smoother communication. Make up too many slang words at once and we have the Tower of Babel. And we have the Tower of Babel.