Sie unterrichtet Kinder she teaches children
It is not, how ever, necessary to make the subject first:
Kinder unterrichtet sie she teaches children (with emphasis on children. colloquially it might be translated as "Children are what she teaches")
(Children teach her would be: Kinder unterrichten sie)
Nor is it necessary to make the object first, if the subject is not:
Auch unterrichtet ihr Bruder Kinder Also her brother teaches children
When we say 'verb second', it doesn't mean it has to be the second word, some words group together as a single idea:
Ihr Bruder unterrichtet Kinder auch Her brother teaches children, too
Viele Kinder unterrichtet ihr Vater Her father teaches many children
Jeder Dienstag unterrichtet sie ein Kind Every Tuesday she teaches a child
There are two instances where the 'verb second' rule does not apply. The first is questions. Questions, like in English, always have the verb preceding the subject. This will often make the Verb come first, but not always:
Unterrichtet ihr Bruder auch Kinder? Does her brother also teach children?
Warum unterrichtet sie jeder Dienstag ein Kind? Why does she teach a child every Tuesday?
The other instance where the verb doesn't go second is in the Imperative, when giving orders:
When ordering some one you would normally use 'du' with, you simply use the root:
Lern! Learn!; Arbeit!Work!; Sei! Be!**
When ordering people you would normally use 'ihr' with, you simply use the ihr-form:
Lernt! Learn!; Arbeitet! Work!; Seid! Be!
When ordering people you would normally use 'Sie' with, you use the infinitive and the 'Sie':
Lernen Sie! Learn!; Arbeiten Sie! Work!; except: Seien Sie! Be!
*This refers to the first verb in the sentence. All subsequent verbs go at the end of the sentence, but we don't really need to know that yet...
**Imperative du forms can be softened by adding an -e to the end of the word: Lerne!; Arbeite!; Seie!