Çocuk portakal suyunu pipetle içiyor.

Because portakal suyunu is the definite direct object of the sentence.

• portakal suyu = orange juice
• portakal suyunu = the orange juice / orange juice as a specific object being acted on

In Turkish, a specific/definite direct object usually takes the accusative ending.

Here is the breakdown:

• portakal suyu = orange juice
• portakal suyu + -(n)u = portakal suyunu

The -nu part is the accusative ending here. The extra n is a buffer consonant that appears in this kind of form.

Compare:

• Çocuk portakal suyu içiyor. = The child is drinking orange juice.
  → more general / indefinite
• Çocuk portakal suyunu içiyor. = The child is drinking the orange juice.
  → specific juice

This is a very common Turkish noun-compound pattern.

Turkish often says things like:

• elma suyu = apple juice
• üzüm suyu = grape juice
• portakal suyu = orange juice

Literally, portakal suyu looks like orange water/juice, with su meaning water and suyu being the compound form.

The pattern is:

• Noun + Noun-(s)I

So:

• portakal + suyu

This does not mean literal possession in the normal English sense. It is just the standard way Turkish builds compounds like food and drink names.

pipetle means with a straw or using a straw.

Turkish can express with by attaching -le / -la directly to a noun:

• pipet = straw
• pipetle = with a straw

This ending can mean:

• together with
• by means of
• using

In this sentence, it is the instrumental/comitative meaning: using a straw.

You can also see the separate form ile:

• pipet ile = with a straw

But in everyday Turkish, the attached form is extremely common.

içiyor comes from the verb içmek, which means to drink.

Breakdown:

• iç- = drink
• -iyor = present continuous suffix

So:

• içiyor = is drinking

This tense is commonly used for actions happening right now, so it matches English is drinking very well.

Depending on context, this form can sometimes also translate as a simple present in English, but in a sentence like this, is drinking is the most natural interpretation.

Turkish does not have articles like English a/an/the.

That means:

• çocuk can mean a child or the child
• context tells you which is meant

For objects, Turkish often shows definiteness through the accusative ending:

• portakal suyu = orange juice / some orange juice
• portakal suyunu = the orange juice / that specific orange juice

So in this sentence:

• çocuk is understood from context
• portakal suyunu is clearly specific because of the accusative ending

Not completely.

The basic neutral Turkish word order is:

• Subject + Object + Verb

So this sentence follows a very normal pattern:

• Çocuk = subject
• portakal suyunu = object
• pipetle = instrument/adverbial element
• içiyor = verb

Turkish word order is fairly flexible, though, especially for emphasis or focus. For example:

• Çocuk pipetle portakal suyunu içiyor.
• Portakal suyunu çocuk pipetle içiyor.

These can all be possible, but they may sound different in emphasis.

The most neutral thing in Turkish is usually to keep the verb at the end.

Yes, that is possible, but the meaning changes slightly.

• Çocuk portakal suyunu pipetle içiyor.
  = The child is drinking the/specific orange juice with a straw.

• Çocuk pipetle portakal suyu içiyor.
  = The child is drinking orange juice with a straw.
  → more general / not marked as specific

So the main difference is not really pipetle; it is whether the object is:

• definite/specific → portakal suyunu
• indefinite/general → portakal suyu

Because Turkish often leaves out subject pronouns when they are unnecessary.

In this sentence, the subject is already stated:

• Çocuk = child

So there is no need to add a pronoun.

If you wanted a pronoun, Turkish would use:

• O portakal suyunu pipetle içiyor.

But o can mean:

• he
• she
• it

Turkish pronouns do not mark gender the way English does.

It is the accusative ending, but this form is a little tricky because the noun is already in a compound form.

Start with:

• su = water
• suyu = its water / juice in the compound portakal suyu

Then when you add the accusative, you get:

• suyu + -(n)u = suyunu

That n is a buffer consonant, which helps connect endings smoothly.

So in the full phrase:

• portakal suyu = orange juice
• portakal suyunu = the orange juice (as the direct object)

This is a very common pattern in Turkish, and learners often notice it in compounds and possessed forms.