A faixa de pedestres fica logo depois do cruzamento, onde uma policial costuma ajudar as crianças.

A is the feminine singular definite article, meaning the.

It is used because faixa is a feminine noun:

• a faixa
• a faixa de pedestres

So A faixa de pedestres means the crosswalk.

De pedestres means something like for pedestrians or pedestrian in a general sense.

Portuguese often uses de + noun to classify something:

• faixa de pedestres = pedestrian crossing
• escova de dentes = toothbrush
• parada de ônibus = bus stop

If you said dos pedestres, it would sound more like of the pedestrians, referring to specific pedestrians, which is not the normal expression here.

Yes, ficar can mean to stay or to become, but it also very commonly means to be located.

In this sentence:

• A faixa de pedestres fica logo depois do cruzamento means
• The crosswalk is located right after the intersection

This is a very common use of ficar when talking about the location of places, buildings, streets, and objects.

Logo depois means right after, soon after, or immediately after.

• depois = after
• logo depois = right after / immediately after

So:

• logo depois do cruzamento = right after the intersection

Also, logo here does not mean logo as in a brand symbol.

Do is a contraction of de + o.

• o cruzamento = the intersection
• de o cruzamento becomes do cruzamento

This kind of contraction is extremely common in Portuguese:

• de + o = do
• de + a = da
• em + o = no
• em + a = na

Yes. Cruzamento means intersection or crossing.

It comes from the idea of things crossing:

• cruzar = to cross
• cruzamento = crossing / intersection

In traffic contexts, cruzamento is a very common word for a road intersection.

Onde means where, and it refers to a place mentioned earlier.

In this sentence, it refers to the location around o cruzamento or the area being described:

• ..., onde uma policial costuma ajudar as crianças = ..., where a police officer usually helps the children

So onde connects the second part of the sentence to that location.

Policial means police officer. It can refer to a man or a woman, and the article shows the gender:

• um policial = a male police officer
• uma policial = a female police officer

Important:

• polícia usually means police as an institution/force, or sometimes police officer in some contexts, but in standard Brazilian Portuguese, policial is the clearest word for police officer
• policia without the accent is a verb form, not the noun used here

So uma policial is exactly right for a female police officer.

Costumar + infinitive expresses a habitual action, something that usually happens.

So:

• costuma ajudar = usually helps
• literally: tends to help / is accustomed to helping

In this sentence, it suggests that the police officer regularly helps the children there, probably as part of a routine.

Because after costumar, Portuguese normally uses the infinitive.

Structure:

• costumar + infinitive

Examples:

• Ela costuma chegar cedo. = She usually arrives early.
• Eles costumam estudar à noite. = They usually study at night.

So:

• uma policial costuma ajudar is the normal structure.

Portuguese often uses definite articles more than English does.

Here, as crianças can mean:

• the children in that context
• or the children the police officer usually helps there, such as local schoolchildren

In English, we often leave articles out more easily, but in Portuguese, using as sounds natural and specific enough in context.

The comma separates the main statement from an added descriptive clause.

Main idea:

• A faixa de pedestres fica logo depois do cruzamento

Extra information:

• onde uma policial costuma ajudar as crianças

So the comma helps show that the second part is additional information about that place. It makes the sentence easier to read and sounds natural in writing.

Sometimes, but fica is more natural here.

• fica is very common for location: is located
• está can also mean is, but it often feels more temporary or less idiomatic in this kind of description

So:

• A faixa de pedestres fica logo depois do cruzamento sounds very natural
• A faixa de pedestres está logo depois do cruzamento is understandable, but less typical

Yes. Some possible alternatives are:

• depois do cruzamento = after the intersection
• logo após o cruzamento = right after the intersection
• após o cruzamento = after the intersection

Among these, logo depois do cruzamento sounds very natural and conversational in Brazilian Portuguese.