Learn Hardcore Ukrainian: Дитині страшно, коли гримить грім. - The child is scared when thunder rumbles.

дитина – nominative (who? what?) – used as the grammatical subject.
дитині – dative (to/for whom?) – used to mark the experiencer of the feeling.

Literally this structure is close to: “To the child, it’s scary.”
The grammatical subject is not explicitly mentioned; it’s an impersonal sentence describing a state that exists for the child, instead of saying “The child is scared” directly with a nominative subject.

What kind of word is страшно here – an adjective or an adverb?

Страшно in this sentence is a predicative adverb (often called a "category of state" word in Slavic grammar). It:

Does not agree in gender or number.
Stays in one fixed form: страшно.
Describes a state: scary / frightening.

It’s similar to English structures like:

It’s scary.
I feel scared.

Other common examples of this pattern in Ukrainian:

Мені холодно. – I am cold.
Йому сумно. – He feels sad.
Нам весело. – We are having fun / feel cheerful.

Could we instead say Дитина боїться, коли гримить грім? What is the difference?

Yes, Дитина боїться, коли гримить грім is grammatically correct and understandable.

Differences in nuance:

Дитині страшно…
- Impersonal construction.
- Focus on the state / feeling itself that arises in the child.
- Neutral, very common in everyday speech.
Дитина боїться…
- Personal verb with дитина as the subject.
- Focus on the child’s active experience of fear (she/he is afraid).
- Slightly more “action-like” / psychological, can sound a bit stronger.

In most everyday contexts, Дитині страшно, коли гримить грім sounds more natural and typical when talking about kids’ reactions.

Why do we say коли гримить грім instead of just коли гримить?

Both are possible:

коли гримить грім – when thunder thunders / when it thunders
коли гримить – also when it thunders

The verb гриміти literally means to thunder / to rumble loudly, and it naturally takes грім as its subject:

Грім гримить. – Thunder is rumbling.

However, in speech грім can be:

Explicit:
- Коли гримить грім, дитині страшно.
Implicit (omitted because it’s obvious from context):
- Коли гримить, дитині страшно.

Adding грім makes the sentence a bit more explicit and perhaps slightly more “textbook-like”. Omitting it is also natural, especially when the topic of weather/thunder is already clear.

Does гримить грім sound redundant, like “thunder thunders” in English?

In English, “thunder thunders” sounds odd and redundant.
In Ukrainian, “грім гримить” is completely normal and idiomatic.

Why?

грім is the noun thunder.
гриміти is the verb to thunder / to rumble.

Ukrainian often uses this natural pairing:

Грім гримить. – Thunder is rumbling.
Дощ іде. – The rain is falling / It’s raining.
Вітер дме. – The wind is blowing.

So “грім гримить” does not feel redundant to a Ukrainian speaker; it feels like a normal subject–verb pair.

Why is there a comma before коли?

In Ukrainian, коли introduces a subordinate clause of time (when…). The rule is:

A main clause and a subordinate clause are separated by a comma.

Here:

Main clause: Дитині страшно – The child feels scared.
Subordinate clause: коли гримить грім – when it thunders.

So we write:

Дитині страшно, коли гримить грім.

If you reverse the order, you also keep the comma:

Коли гримить грім, дитині страшно.

Is коли гримить грім talking about a one-time situation or about what usually happens?

By default, коли + present tense in such sentences often has a general / habitual meaning:

Дитині страшно, коли гримить грім.
→ The child is (generally) scared whenever it thunders.

If you wanted to emphasize one specific event in the future, you could use a future/perfective form:

Дитині буде страшно, коли загримить грім.
→ The child will be scared when the thunder starts / when it thunders (that time).

So in the original sentence, think whenever it thunders rather than at that one moment.

Could we say Дитина злякалася, коли гримів грім instead? What changes in meaning?

Yes, and it changes both tense and aspect:

Дитині страшно, коли гримить грім.
- Present tense, habitual or generally true.
- Describes a repeated / typical reaction.
Дитина злякалася, коли гримів грім.
- злякалася – past, perfective: got scared / became frightened.
- Refers to one completed event: at that time, when it was thundering, the child became afraid.

So:

Original: how the child tends to react in general.
Alternative: what happened once in a particular situation.

How would this sentence look in the plural: “Children are scared when it thunders”?

You change дитині (singular, dative) to дітям (plural, dative):

Дітям страшно, коли гримить грім.
→ Children are scared when it thunders.

Pattern to remember:

дитина → дитині (to/for the child)
діти → дітям (to/for the children)

Is дитина grammatically feminine? What if the child is a boy?

Yes, дитина is a feminine noun in Ukrainian for any child, regardless of the child’s actual sex.

Grammatically, adjectives and past-tense verbs agreeing with дитина take feminine forms:
- Мала дитина злякалася. – The little child (feminine grammar) got scared.

But in the construction Дитині страшно, there is no adjective or agreeing past-tense verb, so gender is not visible at all.

If you need to emphasize the child’s sex, you add another word:

маленький хлопчик – little boy
маленька дівчинка – little girl

Literally, does дитині mean “to the child” or “for the child”? How should I think about the dative here?

The dative case often corresponds to English “to/for someone”, but in this emotional/state construction it’s better to think of it as marking the experiencer:

Мені холодно. – I’m cold. (To me, it’s cold.)
Їй нудно. – She’s bored. (To her, it’s boring.)
Дитині страшно. – The child is scared. (To the child, it’s scary.)

So you can keep “to/for” in mind as a basic dative idea, but understand that here it mainly shows who is experiencing the feeling.

Is the word order fixed? Can I say Коли гримить грім, дитині страшно or Страшно дитині, коли гримить грім?

All of these variants are grammatically correct. Ukrainian word order is relatively flexible, and here it mainly affects emphasis:

Дитині страшно, коли гримить грім. – neutral, very natural.
Коли гримить грім, дитині страшно. – emphasizes the condition “when it thunders”.
Страшно дитині, коли гримить грім. – puts emphasis on страшно (It IS scary for the child when…).

For everyday use, the original order is perfectly normal, but it’s good to know you can rearrange elements for stylistic reasons.

How do you pronounce each word, and where is the stress?

Approximate pronunciation with stress marked in uppercase:

Дитині – dy-TY-nee [dɪˈtɪnʲi]
страшно – STRASH-no [ˈstrɑʃnɔ]
коли – ko-LY [kɔˈlɪ]
гримить – hry-MYT’ [ɦrɪˈmɪtʲ]
грім – HREEM [ɦrʲim]

Notes:

Ukrainian и is a central sound [ɪ], somewhere between English i in sit and uh.
г is a voiced h-sound [ɦ], not like English hard g.
р is rolled/trilled.
Stress is important in Ukrainian; moving it can change the word or make it sound strange.