Quando eu trouxer a mamadeira, a bebê vai parar de chorar.

Because after quando referring to a future event, Portuguese normally uses the future subjunctive.

So:

• Quando eu trouxer... = When I bring / when I have brought... in the future
• Quando eu trazer... is incorrect
• Quando eu trago... would sound habitual, like When I bring the bottle, the baby stops crying
• Quando eu trarei... is not the normal structure here

This is one of the big differences from English: after when, English uses a present form for the future, but Portuguese often uses the future subjunctive.

Trouxer is the future subjunctive of trazer.

This form is used after words like:

• quando = when
• se = if
• assim que = as soon as
• logo que = once / as soon as

Examples:

• Quando eu trouxer a mamadeira...
• Se eu trouxer a mamadeira...
• Assim que eu trouxer a mamadeira...

So the sentence uses a very common Portuguese pattern:
quando + future subjunctive

Trazer is irregular, so its future subjunctive is not obvious at first.

A very useful trick is to start from the pretérito perfeito third-person plural:

• eles trouxeram

Then remove -am:

• trouxer-

That gives you the future subjunctive stem. From there:

• eu trouxer
• você/ele/ela trouxer
• nós trouxermos
• vocês/eles/elas trouxerem

So trouxer is simply the correct irregular future-subjunctive form of trazer.

Sometimes yes, but here eu is helpful because trouxer can refer to more than one subject:

• eu trouxer
• você trouxer
• ele/ela trouxer
• a gente trouxer

So if you said only Quando trouxer a mamadeira..., the subject would be less clear unless the context already made it obvious.

Portuguese often drops subject pronouns, but speakers keep them when they want clarity or emphasis. In this sentence, eu sounds very natural.

Bebê can be used with either article, depending on the baby's sex or the speaker's preference:

• o bebê = the baby boy, or sometimes just the baby in a general/default way
• a bebê = the baby girl

In this sentence, a bebê tells you the baby is female.

In real Brazilian Portuguese, you may hear both articles with bebê, especially when people speak casually. But a bebê is absolutely correct for a girl.

Because Portuguese uses articles very naturally with specific nouns, often more often than English does.

Here a mamadeira means the bottle, referring to a specific, understood bottle — most likely the baby's bottle.

Compare:

• a mamadeira = the bottle
• uma mamadeira = a bottle

So the sentence is talking about a particular bottle that both speaker and listener already have in mind.

It breaks down like this:

• vai parar = is going to stop
• de chorar = crying

The key pattern is:

parar de + infinitive = to stop doing something

Examples:

• parar de chorar = stop crying
• parar de falar = stop talking
• parar de correr = stop running

So a bebê vai parar de chorar literally means the baby is going to stop crying.

Because in this meaning, Portuguese uses the fixed pattern:

parar de + infinitive

So you say:

• parar de chorar
• parar de comer
• parar de estudar

Without de, the sentence would be wrong here.

This is just a verb pattern you need to learn as a unit:
parar de fazer algo = to stop doing something

Because ir + infinitive is extremely common in spoken Brazilian Portuguese.

So:

• vai parar = everyday, natural, conversational
• parará = correct, but more formal, written, or literary

Both mean roughly the same thing, but in normal Brazilian speech, vai parar is much more common.

That is why a bebê vai parar de chorar sounds very natural.

Yes. You can also say:

A bebê vai parar de chorar quando eu trouxer a mamadeira.

This means the same thing.

Both orders are natural:

• Quando eu trouxer a mamadeira, a bebê vai parar de chorar.
• A bebê vai parar de chorar quando eu trouxer a mamadeira.

Putting the quando clause first gives it a little more prominence, like setting up the condition or timing first.

Because the sentence begins with a subordinate clause:

Quando eu trouxer a mamadeira

Then comes the main clause:

a bebê vai parar de chorar

In Portuguese, when this kind of time clause comes first, using a comma is standard and natural.

If the clause comes second, the comma is usually omitted:

• A bebê vai parar de chorar quando eu trouxer a mamadeira.

Yes. In Brazilian Portuguese, mamadeira is the normal everyday word for a baby's bottle.

That is one reason this sentence sounds specifically Brazilian. In European Portuguese, you are more likely to hear biberão instead.

So for Portuguese from Brazil:

• mamadeira = the natural choice