Po kolacji dzieci jedzą budyń.

Because the preposition po here means after, and in this meaning it requires the locative case.

• dictionary form: kolacja = dinner / supper
• locative singular: kolacji

So:

• po kolacji = after dinner

This is a very common pattern in Polish:

• po obiedzie = after lunch
• po pracy = after work
• po szkole = after school

Dzieci is in the nominative plural, because it is the subject of the sentence.

The basic structure is:

• dzieci = the children
• jedzą = eat / are eating
• budyń = pudding

So dzieci is the group doing the action.

A useful thing to know is that dzieci is an irregular plural form of dziecko (child).

• singular: dziecko
• plural: dzieci

Jedzą is the 3rd person plural form of the verb jeść (to eat), because the subject is plural: dzieci (children).

Conjugation of jeść in the present tense:

• jem = I eat
• jesz = you eat
• je = he/she/it eats
• jemy = we eat
• jecie = you all eat
• jedzą = they eat

Since children = they, Polish uses jedzą.

In this sentence, budyń is the direct object of jedzą, so we expect the accusative case.

For many masculine inanimate nouns, the accusative singular is the same as the nominative singular. Budyń is one of them.

So:

• nominative: budyń
• accusative: budyń

That is why the form does not change here.

It can mean either, depending on context.

Polish present tense often covers both:

• Children eat pudding after dinner.
• The children are eating pudding after dinner.

Without extra context, the sentence can sound like:

1. a habit / routine, or
2. something happening now

If you wanted to make the ongoing meaning clearer, context would usually do that rather than a special verb form, since Polish does not have a separate am eating / are eating tense like English.

Polish does not have articles like a, an, or the.

So dzieci can mean:

• children
• the children

and budyń can mean:

• pudding
• the pudding
• sometimes even some pudding, depending on context

Polish relies on context much more than English does for this.

Yes. Polish word order is more flexible than English word order, because cases show the grammatical roles.

The neutral order here is:

• Po kolacji dzieci jedzą budyń.

But other orders are possible, for example:

• Dzieci jedzą budyń po kolacji.
• Budyń dzieci jedzą po kolacji.

These versions may sound slightly different in emphasis:

• starting with Po kolacji highlights when
• starting with Dzieci highlights who
• starting with Budyń highlights what they eat

Even though the order can change, the original sentence is a very natural neutral sentence.

Not always exactly. Kolacja usually means the evening meal, so depending on the speaker’s habits and dialect, it may be translated as:

• dinner
• supper

In many learning materials, kolacja is often given as supper or dinner, depending on what sounds most natural in English.

So po kolacji means after the evening meal.

The letter ń is a soft n sound, similar to the ny sound in some pronunciations of canyon, though not exactly the same.

Very roughly:

• budyń sounds like BOO-din' with a softened final n
• dzieci sounds roughly like DJE-chi or JYE-chi, depending on how detailed you want to be with approximation
• jedzą ends with ą, which is a nasal vowel

A few pronunciation notes:

• dzi in dzieci is a soft sound
• ń is not the same as ordinary n
• ą is often pronounced differently depending on what follows it, but learners usually first learn it as a nasal o

Because Polish usually does not need subject pronouns when the verb form already shows who is doing the action.

• jedzą already tells us the subject is they
• dzieci is included because it tells us who those they are

So saying a pronoun as well would usually be unnecessary:

• Po kolacji dzieci jedzą budyń. = natural
• Po kolacji one dzieci jedzą budyń. = incorrect
• Po kolacji one jedzą budyń. = possible only if they has a clear reference from earlier context, but often unnecessary

In Polish, explicit pronouns are mainly used for emphasis, contrast, or clarity.

By itself, it can be either.

It may describe:

• a general routine: After dinner, the children eat pudding
• a current event: After dinner, the children are eating pudding

If you want to understand which one is meant, look at the surrounding context.

For example:

• in a story about daily family life, it probably means a habit
• in a scene describing what is happening now, it probably means a current action

That flexibility is very normal in Polish present tense sentences.