Das Kind sieht eine Schildkröte.

Because Kind is a neuter noun in German, so its basic singular article is das.

German nouns have grammatical gender:

• der = masculine
• die = feminine
• das = neuter

So:

• das Kind = the child

In this sentence, das Kind is also the correct form for both nominative and accusative singular, so the article does not change here.

No. This is one of the most common things English speakers wonder about.

The grammatical gender of Kind is neuter, but that does not mean the real child has no biological sex or identity. German grammatical gender and real-world gender are often different things.

So das Kind can refer to:

• a boy
• a girl
• any child

Later in a conversation, German may switch to a pronoun based on the actual child:

• Das Kind ist müde. Es schläft.
• but also sometimes Das Kind ist müde. Er schläft. / Sie schläft. if the child’s sex is known and relevant

Because Schildkröte is a feminine noun, and the feminine indefinite article in the singular is:

• eine in the nominative
• eine in the accusative

So the form stays the same.

That is why you get:

• eine Schildkröte = a turtle

Compare that with a masculine noun:

• der Hund = the dog
• ein Hund = a dog (nominative)
• einen Hund = a dog (accusative)

So einen is used for masculine accusative, not for feminine nouns like Schildkröte.

In this sentence, the normal German word order helps you:

• Das Kind = subject
• sieht = verb
• eine Schildkröte = direct object

So the child is the one doing the seeing.

English speakers often expect case endings to make this totally obvious, but in this particular sentence both noun phrases look the same in nominative and accusative:

• das Kind can be nominative or accusative
• eine Schildkröte can also be nominative or accusative

So here, word order is especially important.

Because the infinitive is sehen = to see, and the subject das Kind is third person singular.

The present-tense forms are:

• ich sehe
• du siehst
• er/sie/es sieht
• wir sehen
• ihr seht
• sie/Sie sehen

So with das Kind = it / the child, you use:

• das Kind sieht

Also notice that sehen has a stem-vowel change in the 2nd and 3rd person singular:

• e → ie
• sehen → du siehst, er/sie/es sieht

Because German main clauses usually follow the V2 rule: the conjugated verb comes in the second position.

In your sentence:

• Das Kind = first position
• sieht = second position
• eine Schildkröte = the rest

So:

• Das Kind sieht eine Schildkröte.

If you move something else to the front, the verb still stays second:

• Heute sieht das Kind eine Schildkröte.
• Im Zoo sieht das Kind eine Schildkröte.

This is one of the most important word-order rules in German.

Because all nouns are capitalized in German.

So in this sentence:

• Kind is capitalized because it is a noun
• Schildkröte is capitalized because it is a noun

This is different from English, where common nouns are usually not capitalized.

A few helpful pronunciation points:

• sieht: the ie is pronounced like a long English ee sound
  So sieht sounds roughly like zeet with a German z/s-like start depending on accent, but standard German sieht begins with a voiced z sound: zeet

• Sch in Schildkröte sounds like English sh
• ö is a vowel English does not really have; a rough approximation is to say eh while rounding your lips
• The stress is on the first syllable: SCHILD-krö-te

A rough English approximation:

• Schildkröte ≈ SHILT-kruh-tuh, though this is only approximate

The plurals are:

• das Kind → die Kinder
• die Schildkröte → die Schildkröten

So:

• Das Kind sieht eine Schildkröte.
• Die Kinder sehen Schildkröten.

Notice:

• the plural article is die for all genders
• the verb changes too: sehen instead of sieht

Yes, but that means something different:

• Das Kind sieht eine Schildkröte. = the child sees a turtle
• Die Schildkröte sieht das Kind. = the turtle sees the child

So changing the order and the noun phrase changes the meaning.

With your original sentence, the normal interpretation is very clear because German usually presents the subject first in a basic statement.