البنت جابت بالونة حمرا لاخوها الصغير.

A rough pronunciation is:

el-bent gābet balloona ḥamra le-akhūha es-soghayyar

A few helpful notes:

• ج in Egyptian Arabic usually sounds like g, so جابت sounds like gābet
• ال in الصغير is pronounced es- here because ص is a “sun letter,” so the l sound assimilates
• ح in حمرا is a stronger, breathier h than English h

جابت means she brought.

It comes from the verb جاب = to bring / to get in Egyptian Arabic.
The ending -ت shows that the subject is feminine singular.

So:

• جاب = he brought
• جابت = she brought

Since البنت means the girl, the feminine form is used.

That is a very common Egyptian Arabic feature.

In Egyptian Arabic, ج is usually pronounced as a hard g sound, so:

• جابت → gābet

In Modern Standard Arabic, learners are often taught a j-like pronunciation, but Egyptian speech normally uses g.

Arabic does not have an indefinite article like English a / an.

So بالونة by itself can mean a balloon.
If it were البالونة, that would mean the balloon.

Yes. بالونة is treated as feminine.

One big clue is the ending ة, which often marks feminine nouns in Arabic. Because بالونة is feminine, the adjective describing it also has to be feminine:

• بالونة حمرا = a red balloon

Because it is agreeing with بالونة, which is feminine.

In Egyptian Arabic:

• masculine: أحمر or colloquially أحمر
• feminine: حمرا

So حمرا means red for a feminine noun.

This is also a dialect form. In Modern Standard Arabic, the feminine form would be حمراء, but in Egyptian everyday speech and writing, حمرا is very common.

It breaks down like this:

• لـ = to / for
• أخو = brother
• ها = her

So لاخوها means to her brother or for her brother.

With a verb like جابت, English usually says for her brother: The girl brought a red balloon for her little brother.

Because dialect writing is often informal.

In casual Egyptian Arabic spelling, hamzas are very often left out, so:

• لأخوها
• لاخوها

can both appear, especially in informal writing.
So this is normal colloquial spelling, not a mistake.

Because in Arabic, adjectives usually come after the noun they describe.

So:

• بالونة حمرا = a red balloon
• أخوها الصغير = her little brother

This is the normal Arabic pattern, unlike English, where adjectives usually come before the noun.

Because أخوها is already definite.

A noun with a possessive ending like -ها is automatically specific:

• أخوها = her brother

That is already definite, even without ال.
Since the adjective has to match the noun in definiteness, you get:

• أخوها الصغير = her little brother

not:

• أخوها صغير

Because it describes أخوها = her brother, not البنت.

So the agreement works like this:

• البنت → feminine
• أخوها → masculine
• الصغير must match أخوها, so it is masculine

That is why the sentence has both feminine and masculine forms in different places.

No, Arabic word order is fairly flexible.

This sentence uses a very natural Egyptian pattern:

• البنت = subject
• جابت = verb
• بالونة حمرا = object
• لاخوها الصغير = recipient/beneficiary

You could also hear something like:

البنت جابت لاخوها الصغير بالونة حمرا

The meaning stays basically the same, but the focus can shift a little depending on what the speaker wants to emphasize.

Yes, it reads as Egyptian colloquial Arabic.

Some clues are:

• ج pronounced as g
• حمرا instead of Standard Arabic حمراء
• informal spelling like لاخوها

A more standard version would look different, for example:

أحضرت البنت بالونًا أحمر لأخيها الصغير

So the sentence you were given is natural everyday Egyptian Arabic, not formal Standard Arabic.