Learn German: Der Hund hat das Kind nicht verletzt. - The dog did not injure the child.

Verbs that start with an inseparable prefix, like ver-, do not take the usual ge- at the beginning of their past participle. Since verletzen starts with ver-, its past participle is simply verletzt.

Why is nicht placed right before verletzt?

When negating an entire action or sentence in German, nicht usually goes as far to the end of the clause as possible. Here, the final position is occupied by the past participle verletzt, so nicht sits directly in front of it.

Because das Kind looks the same in both the nominative and accusative cases, how do we know it is the object here?

You can tell by looking at the sentence's other noun. Der Hund is explicitly in the nominative case (using the masculine der), which means it has to be the subject doing the action. That leaves das Kind to be the accusative direct object.

Why use the Perfekt tense (hat ... verletzt) instead of the simple past here?

In spoken German and everyday communication, the Perfekt tense is the standard way to talk about completed past events. You would typically only see the simple past (Der Hund verletzte das Kind nicht) in books, written stories, or formal news reports.