Пока малышка дремала в коляске, мама успела купить молоко и хлеб.

Here пока means while or as long as.

In this sentence:

Пока малышка дремала в коляске, мама успела купить молоко и хлеб.
= While the little girl was dozing in the stroller, Mom managed to buy milk and bread.

A learner may already know пока as bye or for now, but here it is a conjunction introducing a time clause.

Дремала is the past tense, feminine singular, imperfective form of дремать (to doze, to nap lightly).

It is used because the baby's dozing is presented as an ongoing background action:

• малышка дремала = the little girl was dozing

That matches English was dozing better than a one-time completed action.

The sentence sets up a time frame:

• while the baby was dozing...

During that time, the mother completed another action.

In the Russian past tense, verbs agree with the subject in gender and number.

• малышка is feminine, so: дремала
• мама is feminine, so: успела

Compare:

• малыш дремал = the little boy was dozing
• мама успела = mom managed
• папа успел = dad managed

So the -а ending in the past tense shows feminine singular.

Малышка is an affectionate word meaning something like:

• little girl
• little one
• baby girl

It comes from малыш / малышка, which refers to a very young child. The form малышка often sounds warm, tender, and natural in family contexts.

So it is not just neutral child; it has a slightly affectionate feel.

В коляске means in the stroller / pram.

Here коляске is in the prepositional case, because в is being used to show location:

• в коляске = in the stroller

Compare:

• в коляске = in the stroller (location, prepositional)
• в коляску = into the stroller (motion toward, accusative)

So the sentence is saying where the baby was dozing, not movement into the stroller.

Успела comes from успеть, which means:

• to manage to do something
• to have time to do something before some limit
• to succeed in doing something in time

So:

мама успела купить молоко и хлеб
means not just Mom bought milk and bread, but more specifically:

• Mom managed to buy milk and bread
• Mom had time to buy milk and bread

There is an implied time limit: she did it while the baby was still asleep/dozing.

After успеть, Russian usually uses a perfective infinitive when the idea is that the action was completed successfully.

So:

• успела купить = managed to buy / managed to finish buying

This fits the meaning perfectly, because the mother completed the purchase.

If you used покупать instead, it would sound wrong or at least unnatural in this context, because покупать is imperfective and focuses on process or repeated action, not successful completion.

They are in the accusative, but for these nouns the accusative looks the same as the nominative.

They are direct objects of купить:

• купить молоко
• купить хлеб

Why no visible change?

• молоко is neuter inanimate, and its accusative singular is the same as nominative.
• хлеб is masculine inanimate, and its accusative singular is also the same as nominative.

So the forms stay:

• молоко
• хлеб

Also, Russian has no articles, so there is no word for a or the here.

Купить is the normal everyday verb for to buy.

• купить = to buy
• приобрести = to acquire / purchase

Приобрести is more formal or bookish in many contexts. For groceries like milk and bread, купить is the most natural choice.

So this sentence sounds very normal and conversational.

Yes. Russian word order is flexible.

This sentence begins with the пока clause to set the scene first:

Пока малышка дремала в коляске, мама успела купить молоко и хлеб.

You could also say:

Мама успела купить молоко и хлеб, пока малышка дремала в коляске.

The basic meaning stays the same.

The original version feels natural because it first gives the background situation (while the baby was dozing...) and then tells what happened during that time.

Yes, that is very strongly implied.

Because of успела, the sentence suggests:

• there was a limited window of time
• the baby was dozing
• the mother completed the shopping within that window

So the idea is something like:

While the baby was napping in the stroller, Mom managed to buy milk and bread before the opportunity ended.

Russian does not explicitly say before she woke up, but that is the natural implication.

Not exactly.

• спать = to sleep
• дремать = to doze, to nap lightly

Дремать suggests lighter, less deep sleep, often for a short time. So it fits well for a baby in a stroller.

That gives the sentence a slightly more specific image than just спала would.

• малышка спала = the little girl was sleeping
• малышка дремала = the little girl was dozing

Both are possible in Russian, but дремала is more precise here.