Waarom staan de kinderen zo hard te schreeuwen?

Both are possible, but they are not exactly the same.

• Waarom schreeuwen de kinderen zo hard? = Why are the children shouting so loudly?
• Waarom staan de kinderen zo hard te schreeuwen? also means that, but it adds a stronger sense of an action that is going on right now.

Dutch often uses verbs like staan, zitten, liggen, and lopen + te + infinitive to describe an ongoing action.

So staan ... te schreeuwen suggests:

• the action is in progress
• and sometimes also that they are literally standing while doing it

In many contexts, staan still keeps a bit of its literal meaning (to stand), but it can also function more like a progressive marker.

Here, te links the infinitive schreeuwen to the verb staan.

This pattern is very common in Dutch:

• staan te + infinitive
• zitten te + infinitive
• liggen te + infinitive
• lopen te + infinitive

Examples:

• Hij staat te praten. = He is standing there talking.
• Ze zit te lezen. = She is sitting reading.
• De hond ligt te slapen. = The dog is lying sleeping.

So in your sentence:

• staan = finite verb
• te schreeuwen = infinitive phrase describing what they are doing

You cannot usually translate this te directly into English. It is just part of the Dutch construction.

Because Dutch main clauses follow the V2 rule: the finite verb must come in the second position.

Here:

• Waarom is in first position
• staan is the finite verb, so it must come second
• de kinderen comes after that

So the structure is:

• Waarom | staan | de kinderen | zo hard te schreeuwen?

This is normal for Dutch question-word questions.

Compare:

• De kinderen staan zo hard te schreeuwen.
• Waarom staan de kinderen zo hard te schreeuwen?

Once waarom moves to the front, the finite verb stays in second position.

It can, but not always as strongly as in English.

In staan te schreeuwen, staan may do two things at once:

1. It can indicate posture: they are standing
2. It can help express an ongoing action

So depending on the context, the sentence may suggest:

• Why are the children standing there shouting so loudly? or simply
• Why are the children shouting so loudly?

If posture is important, Dutch often uses these posture verbs naturally. English usually does this less often.

Yes, hard often means hard in the sense of not soft, but in Dutch it also commonly means loud(ly).

So:

• hard praten = speak loudly
• hard lachen = laugh loudly
• hard schreeuwen = shout loudly

This is extremely common in everyday Dutch.

There is also luid, which is closer to English loud, but hard is often more natural in ordinary speech.

So:

• zo hard te schreeuwen = shouting so loudly

Zo hard means so loudly or that loudly.

• zo = so
• hard = loudly

Together they intensify the idea:

• Waarom schreeuwen ze zo hard? = Why are they shouting so loudly?

It often implies that the speaker finds the volume surprising, annoying, or excessive.

Because kinderen is a plural noun, and in Dutch the definite article for all plurals is de.

So:

• het kind = the child
• de kinderen = the children

This is a very useful rule:

• singular nouns can be de or het
• plural nouns are always de

Schreeuwen can cover several English verbs, depending on context:

• to shout
• to yell
• to scream

In this sentence, the best translation is probably shouting or yelling, unless the context is more dramatic or frightened, in which case screaming could also fit.

Dutch schreeuwen is broader than any single English word here.

Dutch does not form the progressive in the same way English does.

English:

• The children are shouting

Dutch usually just uses the simple present:

• De kinderen schreeuwen

If Dutch wants to emphasize that the action is happening right now, it often uses another construction, such as:

• De kinderen zijn aan het schreeuwen
• De kinderen staan te schreeuwen

So Dutch does not normally say zijn schreeuwend or use zijn the way English uses to be + -ing.

Yes, absolutely.

Waarom zijn de kinderen zo hard aan het schreeuwen? is very natural and also means Why are the children shouting so loudly?

Compare the two:

• Waarom staan de kinderen zo hard te schreeuwen?

  • often suggests ongoing action
  • may also hint that they are literally standing

• Waarom zijn de kinderen zo hard aan het schreeuwen?

  • focuses on the ongoing action
  • does not suggest posture

Both are common. The version with staan feels a bit more vivid and can sound slightly more expressive.

Yes, very easily.

The combination of:

• waarom
• zo hard
• and the progressive feel of staan ... te schreeuwen

often gives the sentence an annoyed, surprised, or complaining tone:

• Why are the children shouting so loudly?

Of course, tone of voice and context matter, but many native speakers would naturally hear some irritation or concern in it.