Á leikvellinum voru sautján börn í gær, en í dag eru þar átján.

Because Icelandic uses prepositions somewhat idiomatically with places.

With leikvöllur (playground), the normal expression is á leikvelli / á leikvellinum, meaning at/on the playground. Icelandic often uses á for open areas, grounds, fields, and similar places.

Using í would suggest being inside something enclosed, so it would not be the normal choice for an ordinary playground.

The dictionary form is leikvöllur. In this sentence it becomes leikvellinum for two reasons:

1. á takes the dative when it shows location.
2. The noun is definite: the playground.

So:

• leikvöllur = playground
• á leikvelli = on/at a playground
• á leikvellinum = on/at the playground

The ending -num is part of the definite dative singular form.

A useful contrast:

• á leikvellinum = at the playground, already there
• á leikvöllinn = onto the playground, movement toward it

This is because Icelandic is a verb-second language in main clauses.

That means the finite verb usually comes in the second position, no matter what comes first.

Here, the sentence begins with Á leikvellinum. Since that first slot is already taken, the verb voru must come next:

• Á leikvellinum — first element
• voru — second element
• sautján börn — subject

A more neutral subject-first version would be:

• Sautján börn voru á leikvellinum í gær.

Both are grammatical, but the given sentence puts focus first on the location.

Because Icelandic does not always need an expletive subject like English there.

English often says:

• There were seventeen children...

But Icelandic can simply start with the location or another adverbial:

• Á leikvellinum voru sautján börn...

You can also say:

• Það voru sautján börn á leikvellinum í gær.

So the sentence without það is perfectly natural. Icelandic has more freedom here than English.

They are two different tenses of vera (to be):

• eru = are (present plural)
• voru = were (past plural)

The sentence contrasts yesterday and today, so the first clause uses the past and the second uses the present.

A quick comparison:

• barnið er = the child is
• börnin eru = the children are
• barnið var = the child was
• börnin voru = the children were

Because barn is singular and börn is plural.

• barn = child
• börn = children

Since the sentence is talking about seventeen children, Icelandic uses the plural noun.

This is also a good word to memorize as an irregular plural:

• singular: barn
• plural: börn

Usually no. In modern Icelandic, numbers like sautján (seventeen) and átján (eighteen) are generally indeclinable, so they stay the same.

What may change is the noun after them.

For example:

• sautján börn = seventeen children
• með sautján börnum = with seventeen children

Here the number stays sautján, but börn changes to börnum because of case.

This is different from lower numbers such as einn, tveir, þrír, and fjórir, which do inflect more.

Because Icelandic, like English, often leaves out a repeated noun when it is already clear from context.

So:

• en í dag eru þar átján

means the same as:

• en í dag eru þar átján börn

The noun börn is understood from the first clause, so it does not have to be repeated.

This kind of omission is very natural.

Þar means there.

It refers back to á leikvellinum from the first clause, so the speaker does not need to repeat the full location.

So the structure is basically:

• á leikvellinum = on the playground
• þar = there, in that place

Without þar, the sentence would feel less anchored to the location already mentioned.

Again, this is the verb-second rule.

Since Í dag is placed first, the finite verb must come second:

• Í dag — first element
• eru — second element
• þar — after the verb

So:

• Í dag eru þar átján. ✅
• Í dag þar eru átján. ❌

If you wanted þar first, you would need a different order, for example:

• Þar eru átján í dag.

That is possible, but it gives a different emphasis.

Because time expressions in Icelandic are fairly flexible in position.

The speaker puts í dag first to highlight the contrast with í gær:

• yesterday: í gær
• today: í dag

By fronting í dag, the second clause sounds more contrastive and stylistically smoother after en.

Other word orders are possible, but the one in the sentence is very natural for a comparison.

En means but or and/but, and it marks a contrast.

The sentence is comparing two situations:

• yesterday: seventeen
• today: eighteen

Because there is a contrast in time and number, en is a very natural conjunction here.

Using og (and) would be grammatically possible in some contexts, but en fits the contrast much better here.