A criança coça a testa e resmunga porque está cansada.

Here a means the.

In Portuguese:

• a = feminine singular definite article = the
• uma = feminine singular indefinite article = a/an

So:

• A criança = the child
• Uma criança = a child

This is a very common point of confusion for English speakers because a looks like the English indefinite article, but in Portuguese it can be the feminine form of the.

Because criança is a grammatically feminine noun in Portuguese.

That means it normally takes:

• the article a
• feminine adjective forms such as cansada

So:

• A criança está cansada

This is true even if the child is a boy. In Portuguese, grammatical gender and real-life sex are not always the same thing. The noun criança is feminine as a word, so agreement is normally feminine.

They are all third-person singular present tense verb forms, matching the singular subject a criança.

Base forms:

• coçar = to scratch / rub
• resmungar = to grumble / mutter / whine
• estar = to be

So:

• coça = scratches / rubs
• resmunga = grumbles / mutters
• está = is

The subject is singular, so Portuguese uses singular verb forms throughout.

The ç is there to keep the s sound.

In Portuguese spelling:

• c before a, o, or u normally sounds like k
• ç before a, o, or u gives the s sound

So:

• coça is pronounced with an s sound
• if it were written coca, it would sound very different

The cedilla is purely a spelling device to preserve pronunciation.

With body parts, Portuguese often uses the definite article rather than a possessive adjective when the owner is obvious.

So:

• coça a testa literally = scratches/rubs the forehead
• but in natural English we usually say scratches/rubs his/her forehead

Portuguese does this a lot with body parts:

• lavou as mãos = washed his/her hands
• fechou os olhos = closed his/her eyes

You can say a sua testa, but that is less neutral here and would usually add emphasis or contrast.

Usually coçar means to scratch, especially because something itches.

But in real sentences, especially with gestures like coçar a testa, it can feel closer to:

• scratch
• rub
• scratch at
• rub absent-mindedly

So in this sentence it suggests a natural tired or irritated gesture involving the forehead. Depending on the translation style, scratches her forehead or rubs her forehead could both work.

Resmunga comes from resmungar, which means something like:

• to grumble
• to mutter
• to complain under one’s breath
• sometimes to whine

It suggests low, dissatisfied speech rather than speaking clearly or loudly.

So the child is not just talking; the child is making annoyed, tired little complaints or muttering sounds.

Because here it means because and introduces a reason:

• porque está cansada = because she/he is tired

This is the normal spelling for giving an explanation or cause.

It is useful to compare:

• porque = because
• por que = why / for what reason
• o porquê = the reason
• por quê = why, at the end of a question

In this sentence, porque is correct because the second part explains the reason for the child’s behaviour.

Portuguese uses estar for a temporary state or condition, and being tired is normally temporary.

So:

• está cansada = is tired

Using ser here would not be the normal way to say someone is tired at the moment. As a general rule:

• ser = more permanent identity or characteristic
• estar = current state, condition, or situation

That is why estar cansado/a is the standard expression for to be tired.

In European Portuguese, estar a + infinitive is the usual progressive form:

• está a coçar a testa
• está a resmungar

But the simple present can also be used for:

• description
• storytelling
• summaries
• scene-setting
• captions

So:

• A criança coça a testa e resmunga... sounds like a descriptive or narrative sentence
• A criança está a coçar a testa e a resmungar... would put stronger emphasis on the actions happening right now

Both are possible, but they do not feel exactly the same.

The accent is part of the correct spelling of this verb form.

It helps show that:

• this is the form está from estar
• the stress falls on the last syllable

It also distinguishes it from other words such as esta, which means this in the feminine singular:

• esta criança = this child
• está cansada = is tired

So the accent is important both for pronunciation and for meaning.