Minha filha come cereal com leite antes de sair para a escola.

Because filha is a feminine noun, so the possessive has to match it:

• meu filho = my son
• minha filha = my daughter

In Portuguese, possessives usually agree with the thing possessed, not with the owner.

In Brazilian Portuguese, the definite article before a possessive is often optional.

So both of these are possible:

• Minha filha...
• A minha filha...

In Brazil, leaving out the article is very common, especially in everyday speech and writing. In European Portuguese, the article is used more consistently.

Yes. Come here is from the verb comer = to eat.

It is the third-person singular form in the present tense:

• eu como = I eat
• você/ele/ela come = you/he/she eats

So minha filha come means my daughter eats.

This often surprises English speakers because come looks exactly like the English verb come, but it has nothing to do with that here.

Because in Portuguese, cereal is commonly used as a mass noun when talking about breakfast cereal.

So:

• come cereal = eats cereal

You can use the plural cereais in some contexts, but for the food someone is eating in a bowl, cereal in the singular is very natural.

It literally means with milk.

So:

• cereal com leite = cereal with milk

This is the normal way to say it in Portuguese. Portuguese often uses com exactly where English uses with.

Because antes is followed by de when it means before in this kind of structure.

So the pattern is:

• antes de + infinitive
• antes de sair = before leaving / before going out

Other examples:

• antes de comer = before eating
• antes de dormir = before sleeping

So antes sair would be incorrect here.

Because Portuguese often uses the infinitive after a preposition like de.

Here the subject of both actions is the same person:

• Minha filha come...
• [Minha filha] sair...

Since it is the same subject, Portuguese naturally uses the infinitive:

• antes de sair

If you wanted to name a different subject, you could do that too, for example:

• antes de ela sair = before she leaves

Because Portuguese usually uses the article with escola:

• a escola = the school

So para a escola is literally to the school, but in natural English the translation is often just to school.

This is a very common difference between English and Portuguese. Portuguese often keeps the article in places where English drops it.

Both can work, but they focus on slightly different things.

• sair para a escola = to leave for school / to head out for school
• ir para a escola = to go to school

With sair, the emphasis is on the moment of leaving home or leaving wherever she is. In this sentence, that fits well with antes de sair.

Yes. In everyday Brazilian speech, para is often shortened:

• para → pra

So you may hear:

• Minha filha come cereal com leite antes de sair pra escola.

That is very common in speech and informal writing. The full form para a escola is more standard in careful writing.

The lh sound is one English speakers often need to practice.

• filha sounds roughly like FEEL-ya, but not exactly
• the lh is a soft palatal sound, similar to the lli in million for some English accents

So:

• fi-lha
• approximate pronunciation: FEE-lya

It is the same sound you hear in words like:

• trabalho
• mulher does not have this sound, so do not assume every l behaves that way

Yes. Portuguese allows some flexibility.

For example, this is also natural:

• Antes de sair para a escola, minha filha come cereal com leite.

That puts the time expression first: Before leaving for school, my daughter eats cereal with milk.

Both versions are correct. The original sentence sounds very natural in everyday Portuguese.