A melancia tinha muitas sementes, então meu filho comeu só um pouco.

A melancia uses the definite article a because the speaker is talking about a specific watermelon, not watermelons in general.

• A melancia tinha muitas sementes = The watermelon had a lot of seeds
• Melancia tem muitas sementes would sound more like a general statement: Watermelon has a lot of seeds

So here a helps show that this is one particular watermelon in the situation.

Tinha is the imperfect form of ter. It is often used for description or background information in the past.

Here, tinha muitas sementes describes the condition of the watermelon: it had many seeds.

Using teve would sound more like a simple completed event, while tinha fits better for setting up the situation that explains what happened next.

So the sentence structure is basically:

• background description: A melancia tinha muitas sementes
• main completed action: meu filho comeu só um pouco

That contrast is very common in Portuguese.

Because sementes is a feminine plural noun.

Agreement in Portuguese works like this:

• singular feminine: muita semente
• plural feminine: muitas sementes

Since semente is feminine, the adjective/quantifier must also be feminine:

• muita
• muitas

If the noun were masculine plural, then you would use muitos.

Here então means so, therefore, or as a result.

It connects the two parts of the sentence:

• A melancia tinha muitas sementes = the reason/background
• então meu filho comeu só um pouco = the result

So it shows a consequence: the watermelon had many seeds, so my son ate only a little.

Depending on context, então can also mean then, but in this sentence so is the best match.

In Brazilian Portuguese, possessives like meu, minha, seu, nosso can appear with or without the article.

So both of these are possible:

• meu filho
• o meu filho

In Brazil, using the article is very common in everyday speech, but leaving it out is also correct and natural, especially in more neutral or concise style.

So meu filho comeu só um pouco is completely normal.

Comeu is the preterite form of comer, and it shows a completed action:

• comeu = ate

That fits here because the sentence tells us what the son actually did in response: he ate only a little.

If you used comia, that would suggest a habitual, ongoing, or repeated action in the past:

• meu filho comia só um pouco = my son used to eat only a little / was eating only a little

So comeu is the natural choice for a one-time completed action.

Só um pouco means only a little.

• só = only
• um pouco = a little

Together they limit the amount very clearly: he ate only a little

In casual Brazilian Portuguese, só is extremely common. You could also say somente um pouco, but só um pouco sounds more everyday and natural.

Because the thing being eaten is already understood from context: it is the watermelon.

Portuguese often leaves out a noun when it is obvious. So:

• meu filho comeu só um pouco = my son ate only a little
• understood meaning: only a little of it / only a little of the watermelon

If you wanted to make it explicit, you could say:

• meu filho comeu só um pouco da melancia
• meu filho comeu só um pouco dela

But in the original sentence, leaving it out sounds natural and efficient.

Yes. Somente and só can both mean only.

So these are both correct:

• meu filho comeu só um pouco
• meu filho comeu somente um pouco

The difference is mostly style:

• só = more common in everyday speech
• somente = a bit more formal or emphatic

In normal conversation, só is probably what you will hear more often.

Not completely, but the original order is very natural.

These are possible:

• meu filho comeu só um pouco
• meu filho só comeu um pouco
• meu filho comeu um pouco só — more colloquial, often with spoken emphasis

The meaning can shift slightly depending on what is being emphasized.

For example:

• comeu só um pouco emphasizes the small amount
• só comeu um pouco can sound like all he did was eat a little or still emphasize the limitation, depending on context

So the original sentence is a very safe and natural version.

The comma separates two linked clauses:

• A melancia tinha muitas sementes
• então meu filho comeu só um pouco

In writing, this comma helps show the pause and the logical connection between cause and result. It is very natural to punctuate it this way.

You may also see similar connectors separated by commas, such as por isso, então, and assim.

Yes, both contain sounds that are important in Portuguese.

• tinha has nh, which sounds like the ny in canyon
• filho has lh, which sounds like the lli in million for many English speakers, though not exactly the same

A rough pronunciation guide:

• tinha ≈ TEEN-ya
• filho ≈ FEE-lyoo or FEE-lyu

These are only approximations, but they help.

Also:

• então has a nasal sound at the end
• só has an open o sound and the accent mark shows the stressed syllable

These sound patterns are very typical in Brazilian Portuguese.

Not in the same structure.

The original sentence is built as:

• cause first: A melancia tinha muitas sementes
• result second: então meu filho comeu só um pouco

That naturally gives so: The watermelon had many seeds, so my son ate only a little.

If you want because, you would usually reverse the logic:

• Meu filho comeu só um pouco porque a melancia tinha muitas sementes.

That means: My son ate only a little because the watermelon had many seeds.

So both ideas work, but the sentence structure changes.