Το πορτοκαλί μπαλόνι είναι για το μικρό αγόρι.

Because Greek usually uses the definite article the more often than English does.

• το πορτοκαλί μπαλόνι = the orange balloon
• το μικρό αγόρι = the little boy

Each noun phrase normally gets its own article. So if both balloon and boy are definite, both usually need το.

Also, το is the neuter singular form of the, which matches both μπαλόνι and αγόρι, since both are neuter nouns.

Πορτοκαλί is one of the color words in Greek that is often indeclinable, meaning it does not change its ending.

So you can say:

• το πορτοκαλί μπαλόνι = the orange balloon
• η πορτοκαλί τσάντα = the orange bag
• ο πορτοκαλί τοίχος = the orange wall

Unlike many adjectives, πορτοκαλί often stays the same no matter what noun it describes.

This is very common with some color words, especially ones that originally came from nouns, like πορτοκάλι meaning orange.

Because μικρό has to agree with αγόρι.

In Greek, adjectives change form to match the noun in:

• gender
• number
• case

Here, αγόρι is:

• neuter
• singular
• accusative form after για

So the adjective must also be neuter singular accusative, which is μικρό.

Compare:

• το μικρό αγόρι = the little boy
• η μικρή κοπέλα = the little girl
• ο μικρός άντρας = the little man

In Greek, grammatical gender and real-life sex are not always the same thing.

The noun αγόρι means boy, but grammatically it is neuter. That is why it takes:

• το instead of ο
• μικρό instead of μικρός

This is just something you learn with the noun. Many Greek nouns for people are masculine or feminine, but some are neuter, and αγόρι is one of them.

Here είναι για means is for in the sense of is intended for or is meant for.

So:

• Το πορτοκαλί μπαλόνι είναι για το μικρό αγόρι = The orange balloon is for the little boy

This use of για is very common when talking about who something is meant for.

Examples:

• Αυτό είναι για σένα = This is for you
• Το δώρο είναι για τη Μαρία = The gift is for Maria

Yes. The preposition για is followed by the accusative case.

So after για, the noun phrase goes into accusative. In this sentence:

• για το μικρό αγόρι

For neuter nouns like αγόρι, the nominative and accusative often look the same, so you may not notice a visible change.

Compare with a masculine example, where the form changes more clearly:

• ο μικρός φίλος = the little friend
• για τον μικρό φίλο = for the little friend

So yes, για governs the accusative.

Because that is a very normal Greek word order for adjectives.

• το μικρό αγόρι = the little boy
• το πορτοκαλί μπαλόνι = the orange balloon

In Greek, many adjectives commonly come before the noun, especially in simple descriptive phrases.

Sometimes Greek can place adjectives after the noun too, but before the noun is the most basic pattern for beginners.

In Modern Greek, μπ is often used to represent a b sound, especially at the beginning of a word.

So μπαλόνι is pronounced roughly like:

• ba-LO-ni

The stress is on λό.

This is useful because the Greek letter β is pronounced like English v, not English b. So Greek often uses μπ to write the b sound.

Examples:

• μπαμπάς = dad
• μπάνιο = bath / bathroom
• μπαλόνι = balloon

The accent marks show which syllable is stressed.

In your sentence:

• πορτοκαλί → stress on λί
• μπαλόνι → stress on λό
• είναι → stress on εί
• μικρό → stress on ρό
• αγόρι → stress on γό

Stress matters in Greek pronunciation, and sometimes it can even help distinguish forms.

So when learning vocabulary, it is a good idea to learn the accent together with the word.

Yes, Greek word order is often more flexible than English word order.

The most neutral order here is:

• Το πορτοκαλί μπαλόνι είναι για το μικρό αγόρι

But you might also hear something like:

• Για το μικρό αγόρι είναι το πορτοκαλί μπαλόνι

That version puts more emphasis on for the little boy.

Even though Greek allows movement for emphasis or style, the original sentence is the safest and most natural pattern for a learner.

Usually not if you mean the little boy.

• για το μικρό αγόρι = for the little boy
• για μικρό αγόρι = for a little boy

So leaving out the article changes the meaning from definite to a more indefinite or general sense.

Greek uses articles very regularly, so it is important not to drop them when English might also use the.

Yes, in normal usage it simply means orange balloon.

Literally, πορτοκαλί comes from the word for orange, but as an adjective it works just like a color word. You do not need to think of it as a longer expression like orange-colored unless you want to analyze it very literally.

So:

• το πορτοκαλί μπαλόνι is the natural way to say the orange balloon

A natural plural version would be:

• Τα πορτοκαλί μπαλόνια είναι για τα μικρά αγόρια
  = The orange balloons are for the little boys

Notice the changes:

• το → τα
• μπαλόνι → μπαλόνια
• αγόρι → αγόρια
• μικρό → μικρά

But πορτοκαλί stays the same, because it is usually indeclinable.