Как ни рано мы вышли, у ворот уже стояли люди с детьми и смотрели на голубей.

This is a set expression meaning however early or no matter how early.

So:

• Как ни рано мы вышли = However early we left
• more naturally in English: No matter how early we left

The pattern как ни + adverb/adjective is used to show that even an extreme condition did not change the result.

Examples:

• Как ни трудно, надо продолжать. = However hard it is, one must continue.
• Как ни быстро он бежал, он опоздал. = No matter how fast he ran, he was late.

In your sentence, the idea is: Even though we left very early, there were already people there.

Рано is an adverb, meaning early. It describes the action вышли (left/went out), not a noun.

So:

• рано = early (adverb)
• ранний / ранняя / раннее = early (adjective)

Compare:

• Мы вышли рано. = We left early.
  (adverb, describes the verb)
• Ранний поезд ушёл. = The early train left.
  (adjective, describes поезд)

In Как ни рано мы вышли, the word is adverbial because it tells us how early the action happened.

Here ни is not a normal separate negation like English not. In this construction, как ни works together as a concessive expression: however..., no matter how...

So ни helps create the meaning of concession:

• Как ни старался... = However much he tried...
• Как ни странно... = Strange as it may seem / however strange...

You should think of как ни as one pattern rather than translating ни by itself.

Вышли is perfective past plural from выйти, meaning went out / left as a completed action.

Russian often uses:

• perfective for a single completed event
• imperfective for process, repetition, or background action

Here, leaving happened once, so вышли is natural:

• Мы вышли рано. = We left early.

If you said выходили, it would usually suggest repeated leaving, process, or some other context:

• Мы часто выходили рано. = We often left early.
• Когда мы выходили, шёл дождь. = When we were going out, it was raining.

So in this sentence, вышли fits the idea of we set out / left at a particular time.

У ворот means by the gate or at the gate.

The preposition у requires the genitive case.
The noun here is ворота (gate, literally a plural-form noun), and its genitive plural is ворот.

So:

• ворота = gate(s)
• у ворот = at/by the gate

This noun is a little special because ворота is one of those Russian nouns that usually appears only in the plural form, even when English uses singular gate.

Compare:

• у дома = by the house
• у двери = by the door
• у ворот = by the gate

Some Russian nouns are grammatically plural even when English usually thinks of them as a single object. Ворота is one of them.

It refers to a gate, often understood as a two-part structure or as a set of gate doors. Russian treats it as a plural-form noun.

Other similar examples:

• ножницы = scissors
• часы = clock/watch
• брюки = trousers

So although English says at the gate, Russian says у ворот, using the plural-based noun ворота.

Уже means already.

It emphasizes that something had happened sooner than expected.

In this sentence:

• у ворот уже стояли люди = there were already people standing at the gate

This creates the contrast:

• we left very early
• but there were already people there

So уже is important because it shows surprise or contrast with the idea of leaving early.

Russian often uses specific position/state verbs where English uses be.

• стоять = to stand
• сидеть = to sit
• лежать = to lie

So у ворот уже стояли люди literally means: At the gate people were already standing

English could translate this as:

• there were already people standing at the gate
• or more naturally: there were already people at the gate

Russian prefers the more vivid verb стояли, showing their physical position.

Because the subject is люди (people), which is plural.

So both verbs agree with люди:

• люди стояли = people were standing
• люди смотрели = people were looking

This means: people with children were standing at the gate and looking at the pigeons

The subject stays the same for both verbs, so Russian does not need to repeat люди.

С детьми means with children.

The preposition с here means with, and in this meaning it takes the instrumental case.

So:

• дети = children
• с детьми = with children

Other examples:

• с другом = with a friend
• с друзьями = with friends
• с семьёй = with family

In your sentence, люди с детьми means people with children, probably adults who had children with them.

Grammatically, the main subject is люди (people), so strictly speaking, стояли and смотрели agree with люди.

That means the sentence directly says: the people with children were standing and watching the pigeons

In real life, it may also imply that the children were there and possibly watching too, but grammatically the verbs are attached to люди, not дети.

So the safest reading is: There were adults with children there, and those people were watching the pigeons.

The verb смотреть normally takes на + accusative when it means to look at.

So:

• смотреть на кого? на что?
• на голубей = at the pigeons

The base noun is:

• голуби = pigeons

Accusative plural for animate nouns matches the genitive plural:

• голубей

Compare:

• смотреть на дом = look at the house
• смотреть на мальчика = look at the boy
• смотреть на голубей = look at the pigeons

So this is a normal government pattern of the verb: смотреть на + accusative

Because after на with смотреть, Russian uses the accusative case, not the nominative.

For animate masculine plural nouns, the accusative plural looks like the genitive plural.

So:

• nominative: голуби = pigeons
• accusative: голубей = pigeons (as an object)

That is why:

• Голуби летят. = The pigeons are flying.
  (голуби = subject, nominative)
• Они смотрят на голубей. = They are looking at the pigeons.
  (голубей = object after на, accusative)

The sentence has two parts:

1. Как ни рано мы вышли
   = However early we left / No matter how early we left

2. у ворот уже стояли люди с детьми и смотрели на голубей
   = there were already people with children standing at the gate and looking at the pigeons

So the overall structure is:

concession + main result

In smoother English: No matter how early we left, there were already people with children standing at the gate, looking at the pigeons.

Yes. Russian word order is flexible, though different orders change emphasis.

The given sentence sounds natural and highlights the contrast well:

• Как ни рано мы вышли, у ворот уже стояли люди...

If you changed the order, it might still be grammatical, but the focus would shift:

• Как ни рано мы вышли, люди с детьми уже стояли у ворот...
• У ворот уже стояли люди с детьми, как ни рано мы вышли...
  This is much less natural as written.

The original order is good because:

• у ворот sets the scene first
• уже highlights the surprise
• люди с детьми introduces who was there

Yes, that is the idea.

Смотрели is the imperfective past of смотреть. It presents the action as ongoing, unbounded, or backgrounded.

In the scene:

• they were standing there
• they were watching the pigeons

Both стояли and смотрели describe an ongoing situation at that moment.

If you used a perfective verb, it would usually mean a completed act of looking, which would not fit the scene as well.

So the aspect choice helps paint a picture:

• вышли = one completed action
• стояли, смотрели = ongoing background situation