"The child sees the man."
Translation:Das Kind sieht den Mann.
It is not as easy as that. Consider the preposition "in": "Ich gehe im Wald." - "I go around in the wood." and "Ich gehe in den Wald." - "I go into the wood." It depends on the preposition and the verb. "in" in a static context requires dative and in a dynamic context it requires accusative.