Pannkakor är barnens favorit på söndagar.

Because Swedish is talking about pancakes as a dish in general, not one pancake.

• en pannkaka = a pancake
• pannkakan = the pancake
• pannkakor = pancakes
• pannkakorna = the pancakes

In this sentence, pannkakor means something like pancakes are the children’s favorite on Sundays, so the plural sounds natural, just like in English.

Swedish often uses a bare plural when speaking about things in general.

So:

• Pannkakor är gott. = Pancakes are tasty.
• Pannkakor är barnens favorit. = Pancakes are the children’s favorite.

You do not need a word like the here, because the sentence is not about a specific plate of pancakes. It is about pancakes as a general food.

Barnens means the children’s.

It comes from:

• barn = child / children
• barnen = the children
• barnens = the children’s

So this is the genitive (possessive) form of barnen.

A useful thing to notice is that barn is one of those Swedish nouns where the indefinite singular and plural look the same:

• ett barn = a child
• barn = children
• barnen = the children

Then you add -s to make it possessive:

• barnens favorit = the children’s favorite

Because barnens means the children’s, while barns would mean children’s in a more general, indefinite sense.

Compare:

• barnens favorit = the children’s favorite
• barns favorit = children’s favorite / a favorite of children in general

In this sentence, the speaker most likely means a particular group of children, so barnens is the natural choice.

Because favorit here means favorite thing / favorite choice, and that noun stays singular.

So the structure is:

• X är någons favorit = X is someone’s favorite

Even if X is plural, favorit can still be singular:

• Pannkakor är barnens favorit.
• Blommor är hennes favorit.

In English we often do something similar:

• Pancakes are the children’s favorite.

So this is normal Swedish usage.

In predicate expressions like this, Swedish often leaves out the article.

So:

• Det är min favorit. = It is my favorite.
• Pannkakor är barnens favorit. = Pancakes are the children’s favorite.

Adding an article would usually sound wrong here. Swedish treats favorit almost like a set expression in this pattern:

• vara någons favorit = to be someone’s favorite

It means on Sundays, in the sense of a habitual or repeated action.

• på söndagar = on Sundays / on Sundays in general
• på söndag = on Sunday, usually meaning this coming Sunday or a specific Sunday

So this sentence suggests a routine or tradition:

• Pannkakor är barnens favorit på söndagar.
  = Pancakes are the children’s favorite on Sundays.

Because Swedish usually uses på with days and parts of the week in time expressions.

Examples:

• på måndag = on Monday
• på fredagar = on Fridays
• på helgen = at/on the weekend
• på söndagar = on Sundays

So på söndagar is the normal preposition here.

Yes, but the meaning or emphasis may shift a little.

The original sentence:

• Pannkakor är barnens favorit på söndagar.

This is a normal, neutral sentence.

You could also say:

• Barnens favorit på söndagar är pannkakor.

This puts more focus on barnens favorit på söndagar first, as if answering the question What is the children’s favorite on Sundays?

A key rule in Swedish is that the finite verb usually comes in second position in main clauses. That is why:

• Pannkakor är ...
• Barnens favorit är ...

Both are correct.

Usually, pannkakor sounds more natural here.

Pannkaka in the singular would mean pancake as a singular item or possibly pancake as a dish in a more abstract sense, but in everyday Swedish, when talking about eating pancakes, the plural pannkakor is much more idiomatic.

So:

• Pannkakor är barnens favorit på söndagar. = natural
• Pannkaka är barnens favorit på söndagar. = possible in some contexts, but less natural here

Yes. Favorit is very common and useful.

Examples:

• min favorit = my favorite
• hans favoritfilm = his favorite movie
• Vilken är din favorit? = Which one is your favorite?

In this sentence, favorit is being used on its own, with the meaning favorite thing/food.

A rough pronunciation guide is:

PANN-kah-kor air BAR-nehns fah-voh-REET poh SUN-dah-gar

A few helpful notes:

• ä in är sounds a bit like the e in bed, but longer.
• barnens has stress on the first syllable: BAR-
• favorit is stressed on the last syllable: fah-voh-REET
• söndagar has the vowel ö, which does not exist in English; it is somewhat like the vowel in French deux or German schön

Most naturally, it suggests some specific children already understood from context, because of barnens = the children’s.

If you wanted a more general statement about children as a group, you might say something like:

• Pannkakor är en favorit bland barn på söndagar.
• Pannkakor är barns favorit på söndagar.

But barnens points more toward the children in a particular family or group.