Педиатр сказал, что перед сном лучше дать ребёнку смесь.

Because дать means to give, and with this verb Russian normally uses:

• кому? = to whom? → dative
• что? = what? → accusative

So in дать ребёнку смесь:

• ребёнку = to the child
• смесь = formula / mixture

The dictionary form is ребёнок, but after дать it becomes ребёнку.

Смесь is the direct object of дать, so it is in the accusative case.

The noun смесь is:

• feminine
• inanimate
• third declension

For many feminine inanimate nouns of this type, the nominative and accusative singular are the same. So:

• nominative: смесь
• accusative: смесь

That is why the form does not visibly change.

Because the preposition перед normally takes the instrumental case when it means before / in front of.

So:

• сон = sleep
• сном = instrumental singular of сон

Therefore:

• перед сном = before sleep / before bedtime

This is a very common Russian pattern:

• перед ужином = before dinner
• перед работой = before work
• перед встречей = before the meeting

Here перед сном means before going to sleep or before bedtime.

It does not mean in front of a dream or anything literal like that. Russian often uses сон in expressions connected with sleeping:

• перед сном = before sleep / before bed
• после сна = after sleep
• во сне = in sleep / in a dream

So in this sentence it refers to the time just before the child goes to sleep.

This is about aspect.

• дать = perfective
• давать = imperfective

In лучше дать ребёнку смесь, the perfective дать presents the action as a single complete act: it would be better to give the child formula.

That sounds natural when talking about a recommended action in a specific situation or as a bedtime step.

If you said лучше давать ребёнку смесь, that would sound more like a repeated or habitual recommendation: it’s better to give the child formula regularly / as a general practice.

So:

• лучше дать = better to give (as one complete action)
• лучше давать = better to be giving / better to give habitually

Both can exist, but дать fits this sentence very well.

Лучше literally means better, but in sentences like this it works almost like it is better to.

So:

• лучше дать ребёнку смесь = it’s better to give the child formula

Russian often leaves out an explicit word for it is in the present tense. So there is no separate word here for it is.

You can think of the structure as:

• лучше + infinitive

For example:

• Лучше подождать. = It’s better to wait.
• Лучше не спорить. = It’s better not to argue.

Что here means that and introduces a subordinate clause.

So the sentence structure is:

• Педиатр сказал = The pediatrician said
• что перед сном лучше дать ребёнку смесь = that before sleep it is better to give the child formula

Russian normally puts a comma before что when it introduces this kind of clause.

So the comma is not optional here; it is standard punctuation.

Сказал is the past tense masculine singular form of сказать.

In Russian past tense, the verb agrees with the subject in gender and number.

Here the subject is педиатр, which is grammatically masculine, so we get:

• педиатр сказал = the pediatrician said

If the speaker wanted to make it clearly female, it would be:

• педиатр сказала

Other forms:

• сказали = plural
• сказало = neuter

Yes. Russian word order is fairly flexible, and changing it often changes emphasis, not the basic meaning.

The original sentence is:

• Педиатр сказал, что перед сном лучше дать ребёнку смесь.

You could also hear:

• Педиатр сказал, что лучше дать ребёнку смесь перед сном.

Both mean basically the same thing. The version with перед сном earlier puts a little more focus on the time frame before bed.

Russian often moves adverbial phrases like this for emphasis or rhythm.

In general, смесь means mixture or blend.

But in the context of feeding a baby or small child, смесь very often means infant formula.

So here it does not mean some random mixture. It specifically refers to formula milk / baby formula.

Context is very important with this word.

In Russian, ё is a separate letter, but in many printed texts it is often replaced by е.

So these usually represent the same word:

• ребёнку
• ребенку

The fully correct spelling is ребёнку, and the pronunciation includes the yo sound.

This happens with many common words:

• всё → often written все
• ещё → often written еще
• ребёнок → often written ребенок

For learners, it is useful to know the ё form, because it helps with pronunciation and stress.

Russian has no articles.

So Педиатр сказал can mean:

• The pediatrician said
• A pediatrician said

Which one is correct depends on context.

In real usage, the listener usually understands from the situation whether this is a specific pediatrician already known to both speakers, or just one pediatrician in general.

This is one of the big differences from English: Russian relies more on context and less on articles.