На даче мы собирали чернику и ежевику, пока дети играли у забора.

На даче is the normal Russian expression for at the dacha / at the country house.

Even though дача is a house or summer cottage, Russian usually treats it as a place/property you go to or stay at, so it uses на rather than в:

• на даче = at the dacha
• на дачу = to the dacha

Using в даче would sound unnatural in this context. В would suggest being physically inside a building, but Russians normally say на даче for the general location.

Даче is in the prepositional case.

That is because it follows the preposition на in a location meaning:

• на даче = at the dacha

The dictionary form is дача, and the prepositional singular is даче.

Собирали is the imperfective past form of собирать.

Here it is used because the sentence describes an ongoing background action:

• мы собирали чернику и ежевику = we were picking bilberries and blackberries

This fits well with пока дети играли = while the children were playing.

If you said мы собрали, that would mean we picked / gathered them completely or we finished picking them, which sounds more like a completed result than an activity in progress.

So:

• собирали = were picking, used to pick, kept picking
• собрали = picked, gathered, finished gathering

They are in the accusative case because they are the direct objects of собирали.

We are picking what?

• чернику
• ежевику

Both nouns are feminine and follow the common pattern:

• черника → чернику
• ежевика → ежевику

So the -а changes to -у in the singular accusative.

These are two different berries:

• черника = bilberry, sometimes loosely translated as blueberry
• ежевика = blackberry

A learner should know that черника is often not exactly the same as the large cultivated blueberry common in North America. In many translations, though, blueberry is used because it is more familiar.

Here пока means while.

It connects two actions happening at the same time:

• мы собирали чернику и ежевику
• пока дети играли у забора

So the sense is:

• We were picking berries while the children were playing by the fence.

Be aware that пока can also mean for now or even appear in farewells like Пока! = Bye! But in this sentence, it clearly means while.

Because the whole sentence is in the past.

• собирали = were picking
• играли = were playing

Russian normally keeps the tense consistent here. Since the berry-picking happened in the past, the children’s playing is also expressed in the past.

Забора is in the genitive case because it follows у.

The preposition у usually means:

• by
• near
• beside
• sometimes at someone's place, depending on context

So:

• у забора = by the fence / near the fence

The dictionary form is забор, and the genitive singular is забора.

Yes, depending on context.

The most natural translations are:

• by the fence
• near the fence
• at the fence

All of these can work. The Russian phrase does not necessarily mean the children were touching the fence; it just places them in that area.

Russian word order is flexible, and putting На даче first helps set the scene.

This is very natural in Russian. The sentence begins with the setting:

• На даче = At the dacha

Then it gives the main action:

• мы собирали чернику и ежевику

Then the background simultaneous action:

• пока дети играли у забора

If you changed the order, the meaning would stay similar, but the emphasis might shift. For example:

• Мы собирали чернику и ежевику на даче...

This is still grammatical, but it does not foreground the location in quite the same way.

Yes, normally it is.

Пока introduces a subordinate clause:

• пока дети играли у забора

Russian usually separates this kind of clause with a comma.

So:

• На даче мы собирали чернику и ежевику, пока дети играли у забора.

That comma is standard punctuation.

It can mean many kinds of collecting or gathering, depending on context.

For example, собирать can mean:

• gather berries or mushrooms
• collect stamps
• assemble something
• pack things together

In this sentence, because the objects are berries, собирали naturally means picked / gathered.

Yes, that is the natural impression.

Because both verbs are imperfective past:

• собирали
• играли

the sentence presents both actions as ongoing activities happening at the same time.

It does not strongly focus on when they started or ended. It simply gives the scene: while one activity was going on, the other was also going on.

Russian has no articles, so it does not have direct equivalents of a and the.

Whether something is understood as a fence, the fence, children, or the children depends on context.

So:

• дети can mean children or the children
• у забора can mean by a fence or by the fence

In this sentence, English usually prefers the children and the fence because the situation sounds specific.

Yes. Very often на даче refers to the whole dacha property or dacha setting, not just the inside of the house.

It can mean something like:

• at the country house
• out at the summer place
• on the dacha property

That broader meaning is one reason на sounds natural here.