Learn Hardcore Spanish (Latin America): En la feria hay un coro de niñas y niños que canta canciones tradicionales. - At the fair there is a choir of girls and boys that sings traditional songs.

En usually means in / at and describes location: en la feria = at the fair or in the fairground.
A usually means to, indicating movement toward something: voy a la feria = I’m going to the fair.
Here we’re describing where the choir is located, not movement, so en la feria is correct.

Why do we use hay instead of está in En la feria hay un coro…?

Hay is used to say there is / there are to introduce the existence of something: hay un coro = there is a choir.
Estar (e.g. está, están) is used for the specific location of something that is already known or identified:

El coro está en la feria = The choir is at the fair. (we already know about “the choir”)
Here the sentence is first introducing the choir, so Spanish uses hay.

Why is it un coro de niñas y niños and not un coro de niños only?

In traditional Spanish, niños (masculine plural) can refer to a mixed group of boys and girls.
However, many speakers now prefer to name both genders explicitly for inclusiveness: niñas y niños (girls and boys).
So un coro de niñas y niños emphasizes that the choir includes both girls and boys, instead of using the generic masculine.

Why does the verb appear as canta (singular) and not cantan (plural), even though we have niñas y niños?

The subject of the verb canta is un coro, which is singular, not niñas y niños.
Grammatically, the structure is:

un coro (subject, singular)
de niñas y niños (a prepositional phrase describing the choir; not the subject)
Because coro is singular, the verb must be singular: un coro … que canta.
If you changed the subject to las niñas y los niños, then you’d say que cantan.

What exactly does que refer to in que canta canciones tradicionales?

Here que is a relative pronoun meaning that / which / who.
It refers back to un coro (the choir), so the phrase means:

un coro … que canta canciones tradicionales = a choir … that sings traditional songs.
Even though niñas y niños are people, the que here still grammatically refers to coro as the subject of canta.

Why is it canta canciones tradicionales and not está cantando canciones tradicionales?

Spanish uses the simple present much more often than English does to talk about actions happening now or habitual actions.
So canta canciones tradicionales can mean either:

sings traditional songs (in general), or
is singing traditional songs (right now), depending on context.
You can say está cantando to stress “right now”, but canta alone is already natural and common.

Why is there no article before canciones tradicionales? Why not las canciones tradicionales or unas canciones tradicionales?

In Spanish, when you talk about what someone does in general (an activity, profession, habit), you often omit the article.

Canta canciones tradicionales = sings traditional songs (as a type of music).
Adding an article changes the nuance:
canta las canciones tradicionales = sings the traditional songs (specific songs already known to speaker and listener).
canta unas canciones tradicionales = sings some traditional songs (an unspecified selection).
Here the idea is general, so no article is the most natural.

Could I change the word order and say Hay un coro de niñas y niños en la feria? Is it still correct?

Yes, Hay un coro de niñas y niños en la feria is perfectly correct and common.
Both orders are fine:

En la feria hay un coro… (emphasis on the location: At the fair, there is…)
Hay un coro… en la feria (more neutral; first mention the existence of a choir, then where).
Spanish word order is flexible, and both versions sound natural.

Why don’t we say un coro de los niños instead of de niñas y niños?

De los niños would usually mean “of the children” in a more specific sense, like the children from this school or those particular children.
De niñas y niños describes the type of members the choir has (its composition), not “children belonging to” someone.
So:

un coro de niñas y niños = a choir composed of girls and boys.
un coro de los niños = a choir of the children (already identified children, more specific and a bit different in nuance).

Is feria here more like “fair” (event) or “market”? And is this usage common in Latin America?

In Latin America, feria can mean:

A fair or festival with events, games, performances, etc.
A street market / open-air market (in some countries).
In this sentence, because there is a choir singing traditional songs, it most naturally suggests a fair or festival.
Using en la feria for a local fair or community festival is very common in Latin American Spanish.

If I want to emphasize that it’s a children’s choir, can I say un coro infantil instead of un coro de niñas y niños?

Yes. Un coro infantil means a children’s choir and is very natural and common.

un coro de niñas y niños highlights explicitly that it includes both girls and boys (inclusive wording).
un coro infantil focuses on the age (children’s choir) without listing genders.
Both are correct; it’s just a difference in style and emphasis.

How would the sentence change if it were about several choirs instead of one?

If you want several choirs, you change the noun and the verb to plural:

En la feria hay coros de niñas y niños que cantan canciones tradicionales.
Here:
coros is plural,
que cantan is also plural to agree with coros.
The rest of the structure remains the same.