Which sentence contains correct parallel structure?

at the pre-school, they teach children to speak polite, walk slow, and act fairly.

at the pre-school, they teach children to speak with politeness, walk slowly, and act fair.

at the pre-school, they teach children to speak politely, walk slowly, and act fairly.

at the pre-school, they teach children to speak polite, walk slowly, and act fair.

At the pre-school, they teach children to speak politely, walk slowly, and act fairly.

Explanation:

Parallelism is when phrases in a sentence have identical grammatical structure.

Three verbs speak, walk, and act are respectively modified by the adverbs politely, slowly, and fairly.  This is correct parallel structure.  

The other sentences use adverbs, adjectives, and even a prepositional phrase to modify verbs. Since the grammatical form of these modifiers is different, the sentences do not contain parallel structure.