Em julho, meus filhos estão de férias.

Em julho means in July.

Portuguese commonly uses em with months:

• em janeiro = in January
• em julho = in July
• em dezembro = in December

In this sentence, Em julho sets the time frame for the whole statement.

Because month names normally do not take an article in this kind of expression.

So you say:

• em julho
• em agosto
• em março

If there were an article o, then em + o = no, but that is not the normal pattern with months here.

The comma separates the time expression from the main clause.

Portuguese often uses a comma after a time phrase placed at the beginning of a sentence:

• Hoje, estou cansado.
• No verão, viajamos muito.
• Em julho, meus filhos estão de férias.

The comma is very natural here, although in some short sentences it may sometimes be omitted in informal writing.

Meus filhos means my children / my sons.

Portuguese usually uses possessives directly before the noun:

• meu carro = my car
• minha casa = my house
• meus filhos = my children

Saying just filhos would mean simply children/sons, without showing whose children they are.

Because filhos is a masculine plural noun.

The possessive has to agree with the noun:

• meu filho = my son
• meus filhos = my sons / my children
• minha filha = my daughter
• minhas filhas = my daughters

Even if filhos can sometimes mean children in a mixed group, the grammatical form is still masculine plural.

It can mean either, depending on context.

• Literally, filhos is the masculine plural form.
• It can refer to:
  • sons only, or
  • children in a mixed group of boys and girls

If the speaker has only daughters, they would normally say minhas filhas.

So without more context, meus filhos may be understood as my children.

Because Portuguese uses estar for temporary states or conditions.

Here, being on vacation is a temporary situation, so:

• estão de férias = they are on vacation

Using ser would sound wrong here.

Compare:

• Eles são brasileiros. = They are Brazilian.
  (identity, more permanent)
• Eles estão cansados. = They are tired.
  (temporary condition)

Estão is the 3rd person plural of estar in the present tense.

Conjugation:

• eu estou
• você/ele/ela está
• nós estamos
• vocês/eles/elas estão

Because the subject is meus filhos (plural), the verb must also be plural: estão.

This is just the normal Portuguese expression.

Estar de férias is the standard way to say someone is on vacation / on holiday / off school for a break.

Similar fixed expressions with de are common in Portuguese:

• estar de carro = to be going by car / to be in a car
• estar de folga = to be off work
• estar de pé = to be standing

So de férias should be learned as a set phrase.

In Portuguese, férias is normally used as a plural noun.

So you say:

• Estou de férias.
• Eles estão de férias.
• As férias começam amanhã.

Even when English uses singular vacation, Portuguese uses plural férias.

This is something learners usually just need to memorize.

Yes. In Brazilian Portuguese, both are possible:

• meus filhos
• os meus filhos

However, meus filhos is very common and natural.

Adding the article os can sometimes sound a little more specific or emphatic, but in many everyday contexts either form works.

Yes, absolutely.

That word order is also natural:

• Em julho, meus filhos estão de férias.
• Meus filhos estão de férias em julho.

The difference is mostly emphasis:

• Em julho, ... emphasizes the time first.
• Meus filhos ... starts with the subject and sounds a bit more neutral.

Yes.

In Brazilian Portuguese, férias can refer to:

• school holidays / school break
• work vacation
• general time off

So in meus filhos estão de férias, it very naturally suggests the children are on school break.

In Brazilian Portuguese, julho is approximately pronounced like ZHOO-lyoo.

A rough guide:

• ju sounds like zhoo
• lh is a special Portuguese sound, similar to the lli in million for many English speakers
• o at the end is often a softer oo sound in Brazilian speech

So: julho ≈ ZHOO-lyoo

Not naturally in this sentence, unless the subject is already very clear from context.

Portuguese often allows omitted subjects, but with 3rd person plural this can become unclear:

• Estão de férias. = They are on vacation.

That works only if everyone already knows who they are.

If you are introducing the information, meus filhos estão de férias is much clearer.