Moja córka tuli lalkę, a syn szuka swojego misia.

Because mój changes its form to match the noun in gender, number, and case.

• córka is feminine singular nominative
• so mój becomes moja

Compare:

• mój syn = my son
• moja córka = my daughter

So moja is just the feminine nominative singular form of mój.

Tulić and szukać are the dictionary forms (infinitives): to cuddle / to hold close and to look for.

In the sentence, the verbs are conjugated for 3rd person singular present tense, because the subjects are singular:

• córka tuli = the daughter cuddles / is cuddling
• syn szuka = the son looks for / is looking for

So:

• tulić → tuli
• szukać → szuka

Because lalkę is the accusative singular form of lalka.

The verb tulić takes a direct object, and direct objects are usually in the accusative.

• nominative: lalka
• accusative: lalkę

This is a very common pattern for feminine nouns ending in -a:

• książka → książkę
• kawa → kawę
• lalka → lalkę

Because miś changes form here.

The base form is:

• miś = teddy bear / little bear

In the sentence, it appears as misia because the verb szukać requires the genitive case:

• szukać kogo? czego? = to look for whom? what?

So:

• nominative: miś
• genitive: misia

There is also a small stem change in spelling: ś often becomes si before a vowel ending.

Here it is genitive.

That is an important point, because szukać traditionally takes the genitive, not the accusative.

So:

• syn szuka swojego misia = the son is looking for his teddy bear

The form can be confusing because for many masculine animate nouns, the accusative singular and genitive singular look the same.

For example:

• Widzę misia = I see the teddy bear → accusative
• Szukam misia = I am looking for the teddy bear → genitive

Same form, different case, depending on the verb.

Because Polish usually uses swój when the possessor is the subject of the same clause.

In the second clause, the subject is syn, so:

• syn szuka swojego misia = the son is looking for his own teddy bear

If you said:

• syn szuka jego misia

that would usually suggest someone else’s teddy bear, not the son’s own.

This is one of the most important uses of swój in Polish.

Because swój also has to agree with the noun it describes.

Here it describes misia, and because szukać takes the genitive, the possessive adjective must also be in the genitive singular masculine form:

• nominative: swój miś
• genitive: swojego misia

So swojego matches misia in case, number, and gender.

Because Polish often leaves out possessive words when the meaning is already obvious from context.

The sentence starts with Moja córka..., so it is natural to understand that syn is also my son.

So both of these are correct:

• Moja córka tuli lalkę, a syn szuka swojego misia.
• Moja córka tuli lalkę, a mój syn szuka swojego misia.

The version without mój sounds a little lighter and more natural when the relationship is already clear.

A often connects two ideas with a sense of contrast or comparison.

In this sentence, it is something like:

• and, while, whereas, or sometimes but

So the feeling is:

• My daughter is cuddling a doll, while my son is looking for his teddy bear.

It is not exactly the same as i.

• i = plain and
• a = and/while/whereas, often with contrast

Here a works well because the sentence compares what the daughter is doing with what the son is doing.

Here is the case breakdown:

• moja córka — nominative
  It is the subject of tuli.

• lalkę — accusative
  It is the direct object of tuli.

• syn — nominative
  It is the subject of szuka.

• swojego misia — genitive
  It depends on szuka, because szukać takes the genitive.

So the sentence is a good example of how Polish uses case endings to show grammatical roles.

Yes. Polish word order is fairly flexible because the case endings show who is doing what.

The sentence as given is a very natural, neutral order:

• Moja córka tuli lalkę, a syn szuka swojego misia.

You can move things around for emphasis, for example:

• Lalkę tuli moja córka, a swojego misia szuka syn.

That is still grammatical, but it sounds more marked or literary. For a learner, the original version is the safest and most natural.

Because Polish has no articles.

English needs words like:

• a doll
• the doll

Polish usually just says:

• lalka / lalkę

The exact meaning depends on context. So lalkę can mean a doll or the doll, depending on the situation.

Very often, yes.

Miś literally means little bear or teddy bear, and in everyday Polish it commonly refers to a child’s stuffed bear.

If you mean a real bear as an animal, the normal word is:

• niedźwiedź = bear

So in this sentence, misia naturally sounds like his teddy bear, not a real bear.