Сын уже умеет сам шнуровать кеды, а младшая сестра пока только смотрит.

Сын is in the nominative case because it is the subject of the first part of the sentence: Сын уже умеет... = The son already knows how...

In Russian, the subject of a clause is usually in the nominative:

• сын = son
• сестра = sister

So here:

• Сын умеет
• сестра смотрит

Both сын and сестра are subjects.

Уже means already.

It shows that the boy has reached a new stage: he now has this ability.

So:

• Сын уже умеет... = The son already knows how to...

It often contrasts with something earlier:

• before, he could not do it
• now, he can

The verb уметь means to know how to / to be able to because of skill.

It is normally followed by an infinitive:

• уметь читать = to know how to read
• уметь плавать = to know how to swim
• уметь шнуровать = to know how to lace

So умеет сам шнуровать кеды means that he has the skill to do it.

This is different from мочь, which means can / be able to in a more general sense:

• Он умеет плавать = He knows how to swim
• Он может плавать = He can swim / is able to swim

Сам here means by himself / on his own.

It emphasizes that the boy does not need help:

• Сын уже умеет сам шнуровать кеды = The son already knows how to lace his sneakers by himself.

This word agrees with the person it refers to:

• сам for masculine
• сама for feminine
• сами for plural

Since сын is masculine, we use сам.

In this sentence, сам is placed before the infinitive to emphasize independence in the action:

• умеет сам шнуровать кеды

This sounds natural in Russian. It highlights he himself does the lacing.

You may also see similar patterns such as:

• Она уже умеет сама одеваться = She already knows how to dress herself.
• Ребёнок сам ест = The child eats by himself.

Russian word order is flexible, but this position is very natural here.

Шнуровать is the imperfective verb. It focuses on the general action or skill, not on one completed result.

After уметь, Russian very often uses the imperfective, because we are talking about ability in general:

• уметь читать
• уметь писать
• уметь завязывать шнурки
• уметь шнуровать кеды

If you used зашнуровать, that would sound more like to lace up completely / to finish lacing, with emphasis on completion.

Here the point is not one finished event, but the learned skill, so шнуровать is the natural choice.

Кеды means a type of casual athletic shoe, often translated as sneakers, trainers, or canvas shoes, depending on context.

It is normally used in the plural, because shoes come as a pair:

• кеды = sneakers
• ботинки = boots/shoes
• туфли = shoes

So шнуровать кеды means to lace sneakers / to lace up his sneakers.

Yes, кеды is the accusative plural here, because it is the direct object of шнуровать.

The dictionary form is also кеды, and for inanimate plural nouns, the accusative often looks exactly like the nominative.

So:

• nominative plural: кеды
• accusative plural: кеды

That is why the form does not visibly change.

Compare:

• Я вижу кеды. = I see the sneakers.
• Кеды лежат на полу. = The sneakers are lying on the floor.

Same form, different case function.

А often links two parts that are being contrasted or compared.

Here the sentence compares the two children:

• the son already knows how to do it himself
• the younger sister, for now, only watches

So а works very well because it sets up a contrast:

• Сын уже умеет... , а младшая сестра пока только смотрит.

It is not as simple as and (и), and it is not as strong or oppositional as but (но). It is more like:

• whereas
• while
• and as for...

Here младшая сестра means younger sister.

The adjective младший / младшая / младшее is often used for relative age within a family:

• старший брат = older brother
• младшая сестра = younger sister

In many contexts, it does not necessarily mean youngest in the absolute sense. It usually just means younger than someone relevant in the context.

Also, младшая agrees with сестра:

• сестра is feminine singular
• so the adjective is младшая

Here пока means for now / at the moment / so far, not while.

So:

• пока только смотрит = for now only watches

It shows that the situation may change later. Right now, the younger sister is not doing it herself yet.

Russian пока can have different meanings depending on context:

• Пока! = Bye!
• Пока я читал, он спал. = While I was reading, he was sleeping.
• Я пока не знаю. = I don’t know yet / for now I don’t know.

In this sentence, it clearly means for now.

Только means only.

It limits what the younger sister is doing:

• she is not lacing the shoes herself
• she is only watching

So:

• пока только смотрит = for now she only watches

The combination пока только is very common and means something like:

• so far only
• for now only

Russian can leave the object unstated when it is obvious from context.

Here смотрит means something like:

• is watching
• is just looking on

The sentence already makes it clear that she is watching the boy and/or the action of lacing the sneakers.

If you wanted, you could make the object explicit:

• смотрит на него = watches him / looks at him
• смотрит, как он шнурует кеды = watches how he laces the sneakers

But Russian often leaves this unsaid when it is easy to understand.

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

The given sentence is natural and neutral:

• Сын уже умеет сам шнуровать кеды, а младшая сестра пока только смотрит.

If you move words around, the sentence may still be grammatical, but the focus changes. For example:

• Сын сам уже умеет шнуровать кеды...
• Младшая сестра пока только смотрит...

Russian often uses word order to highlight what is new, contrasted, or emphasized. For a learner, the best approach is:

1. understand the grammar,
2. notice the emphasis,
3. learn the most natural default patterns first.

Yes, English often says his sneakers, but Russian does not always need to.

In context, it is understood that the son is lacing his own sneakers, so Russian simply says:

• шнуровать кеды

If you really wanted to specify, you could say:

• свои кеды = his own sneakers

But Russian often omits possessive words when ownership is obvious from the situation. This is very common, especially with clothing, body parts, and personal belongings.