Barnet kaster sin legeklods på gulvet.

Barnet means the child, while barn means a child or just child in a dictionary form.

Danish often adds the definite article to the end of the noun instead of using a separate word like English the:

• et barn = a child
• barnet = the child

Because barn is a neuter noun, its definite ending is -et.

Not really in the same way English does. This is mostly about grammatical gender, not about whether the child is literally thought of as an it.

In Danish, nouns belong to grammatical genders, mainly:

• common gender
• neuter

Barn happens to be a neuter noun, so you say:

• et barn
• barnet

That does not necessarily mean the speaker is emphasizing that the child is an it. It is just how the noun works grammatically.

Kaster is the present tense of kaste = to throw.

So it can mean either:

• throws
• is throwing

Danish present tense often covers both the simple present and the present progressive, depending on context.

So:

• Barnet kaster sin legeklods på gulvet
  can mean
• The child throws his/her toy block onto the floor
• The child is throwing his/her toy block onto the floor

Because sin is the reflexive possessive. It is used when the thing belongs to the subject of the sentence.

Here, the subject is barnet and the toy block belongs to that same child, so Danish uses sin:

• Barnet kaster sin legeklods ... = The child throws its own toy block ...

If you used hans or hendes, it would usually mean the block belongs to someone else, not to the child who is throwing it.

Compare:

• Barnet kaster sin legeklods. = The child throws its own toy block.
• Barnet kaster hans legeklods. = The child throws his toy block (someone else’s, not the child’s own).

Because sin/sit/sine must agree with the thing possessed, not with the owner.

The possessed noun here is legeklods, and klods is a common-gender singular noun, so the correct form is sin.

The pattern is:

• sin
  • common-gender singular noun
• sit
  • neuter singular noun
• sine
  • plural noun

Examples:

• sin bog = his/her own book
• sit barn = his/her own child
• sine bøger = his/her own books

So:

• sin legeklods is correct
• sit legeklods is not correct

Because possessives like sin, min, din, hans, hendes usually replace the article.

So Danish says:

• sin legeklods = his/her own toy block
• min bog = my book

Not:

• den sin legeklods
• en sin legeklods

This is similar to English, where you say my book, not the my book.

Legeklods is a compound noun, which is very common in Danish.

It is made from:

• lege = play
• klods = block

So legeklods literally means something like play block, i.e. a toy block or building block.

Danish often combines words this way into one noun.

It can suggest either, depending on context, but with kaster it often has the sense of movement onto the floor.

• på usually means on
• gulvet means the floor

So literally, på gulvet is on the floor.

But with a verb like kaste (throw), English often prefers onto the floor, because the action involves movement toward the floor.

So this phrase may be translated naturally as:

• on the floor
• onto the floor

depending on what sounds best in English.

For the same reason as barnet earlier: gulvet is the definite form, meaning the floor.

• et gulv = a floor
• gulvet = the floor

Again, gulv is a neuter noun, so the definite ending is -et.

The basic order is:

• subject
  • verb
    • object
      • adverbial/prepositional phrase

So here:

• Barnet = subject
• kaster = verb
• sin legeklods = object
• på gulvet = prepositional phrase

That gives:

• Barnet kaster sin legeklods på gulvet.

This is a very normal Danish main-clause word order.

If another element is moved to the front, Danish usually follows the verb-second rule, so the verb still stays in second position.