Педиатр сказал, что всё в порядке, но посоветовал чаще менять пелёнку после сна.

In the past tense, Russian verbs agree with the subject in gender and number.

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

• сказал = masculine singular past of сказать
• посоветовал = masculine singular past of посоветовать

If the speaker were clearly referring to a female pediatrician, many speakers would say:

• Педиатр сказала... но посоветовала...

So these verb forms tell you something about the grammatical gender of the subject.

Russian often leaves out subject pronouns when the subject is already clear from context.

So instead of saying:

• Педиатр сказал..., но он посоветовал...

Russian very naturally says:

• Педиатр сказал..., но посоветовал...

English usually repeats he, but Russian does not need to.

Here что is a conjunction, meaning that.

It introduces the clause reporting what the pediatrician said:

• сказал, что всё в порядке = said that everything is fine

This is different from что meaning what in questions or relative clauses.

In the present tense, Russian usually omits the verb быть = to be.

So:

• всё в порядке literally looks like everything in order
• but it means everything is fine / everything is okay

You can think of an unspoken есть, but in normal modern Russian it is simply left out.

В порядке is a very common expression meaning:

• okay
• fine
• in order

Grammatically, it is:

• в
  • prepositional case
• порядок → порядке

So literally it means in order, but idiomatically it often means everything is fine.

Всё means everything.

The letter ё is important here, because:

• всё = everything
• все usually = all / everyone

However, in everyday Russian writing, ё is often replaced by е, so you may sometimes see все в порядке where the intended meaning is still всё в порядке. Context usually makes it clear.

In careful learner materials, ё is often written explicitly to help you.

In standard pronunciation, что is usually pronounced roughly as што, not ч-to.

So in this sentence:

• что всё в порядке

you would normally hear што всё в порядке.

This is one of those very common Russian spelling-pronunciation mismatches that learners simply have to get used to.

Чаще is the comparative form of the adverb часто = often.

So:

• часто = often
• чаще = more often

It modifies the verb менять, so the idea is to change it more often.

Russian often forms comparatives as a single word, where English may use more + adverb.

This is because the advice is about a repeated or habitual action, not one single completed action.

• менять = imperfective, focusing on the process or repeated action
• чаще менять = to change more often

That fits the sentence very well, because чаще already suggests repetition.

If you used a perfective verb such as поменять, it would sound more like a single completed change, which is less natural here.

Because пелёнку is in the accusative singular, which is the case used for the direct object of менять.

The dictionary form is:

• пелёнка

But after менять you need the object form:

• менять пелёнку

For feminine nouns ending in -а, the accusative singular usually changes -а to -у.

Not always.

Пелёнка traditionally means something like:

• a baby cloth
• swaddling cloth
• diaper cloth
• absorbent sheet/pad for a baby

In modern everyday Russian, a disposable diaper is more often:

• подгузник

So depending on context, пелёнка may be translated as diaper, but the Russian word can have a slightly different nuance from modern English diaper.

Because the preposition после always takes the genitive case.

The noun is:

• сон = sleep

Its genitive singular form is:

• сна

So:

• после сна = after sleep / after sleeping / after the nap

This is a very useful pattern to remember:

• после + genitive

There are two main reasons:

1. Comma before что
   Russian puts a comma before a subordinate clause introduced by что:

   • Педиатр сказал, что...

2. Comma before но
   Russian also normally puts a comma before the coordinating conjunction но = but:

   • ..., но посоветовал...

So the punctuation here is completely standard Russian punctuation.