Learn Hardcore Russian: Довольный ребёнок улыбается маме.

улыба- – the verb stem from улыбаться
-ет- – 3rd person singular ending for the present tense (he/she/it)
-ся – reflexive ending (written as -сь after a vowel, -ся after a consonant)

So улыбается = “(he/she/it) is smiling” and literally is “smiles-himself/herself” in form.

If you changed the person:

я улыбаюсь – I am smiling
ты улыбаешься – you are smiling
мы улыбаемся – we are smiling

What is the function of -ся in улыбается? Is it reflexive in meaning?

Yes, -ся is the reflexive marker in Russian. Historically it meant “oneself,” but in many verbs today it doesn’t translate literally as “oneself”; instead, it:

Marks verbs that involve an internal state or spontaneous action:
- улыбаться – to smile
- бояться – to be afraid
- надеяться – to hope
Can make a normally transitive verb intransitive:
- открывать дверь – to open the door
- дверь открывается – the door opens (by itself / is opening)

With улыбаться, you don’t usually say “smile oneself” in English; you just say “smile.” So you usually just treat -ся here as part of the verb form “to smile.”

Why is довольный before ребёнок? Could you also say ребёнок довольный?

Both positions are possible, but they have different nuances.

Довольный ребёнок улыбается маме.
Довольный here is a normal descriptive adjective before the noun. It simply describes what kind of child: the content/satisfied child is smiling at his mom. Neutral, standard description.
Ребёнок довольный улыбается маме.
This sounds more like adding extra comment about the child, similar to “the child, (who is) content, smiles at his mom.” It’s a bit more “afterthought” or expressive in tone, less neutral.

For basic, neutral description, putting the adjective before the noun (довольный ребёнок) is the standard pattern you should learn first.

Why is довольный in the masculine form if the child could be a girl?

In Russian, грамmatical gender follows the noun’s gender, not the real-life person’s gender.

ребёнок is grammatically masculine (even though it can refer to a boy or a girl).

Therefore, any adjective describing ребёнок must also be masculine:

довольный ребёнок – content child (masc.)
маленький ребёнок – small child (masc.)

If you used девочка (girl), which is feminine, the adjective would also be feminine:

довольная девочка – content girl
маленькая девочка – small girl

What is the difference between довольный and счастливый?

Both can be translated as “happy,” but they’re not the same:

довольный – “content, satisfied, pleased”
Suggests that one’s needs or expectations are met.
Example: Ребёнок доволен подарком. – The child is satisfied/pleased with the present.
счастливый – “happy, fortunate, blissful”
Stronger, deeper happiness.
Example: Счастливый ребёнок играет с друзьями. – A happy (in life) child is playing with friends.

In Довольный ребёнок улыбается маме, the idea is more “a content / pleased child” than deeply “ecstatically happy.”

Could I also say Ребёнок доволен instead of Довольный ребёнок? What’s the difference?

Yes, but the grammar and structure change:

Довольный ребёнок улыбается маме.
Довольный is an attributive adjective modifying ребёнок: The content child smiles at his mom.
Ребёнок доволен.
Доволен is a short-form adjective used as a predicate (“the child is content/satisfied”).
You’re stating a current state: The child is content.

You could say:

Ребёнок доволен и улыбается маме. – The child is content and smiles at his mom.

So:

довольный ребёнок – “a content child” (description before the noun)
ребёнок доволен – “the child is content” (state after the noun)

What case is ребёнок in, and how can I tell?

Ребёнок is in the nominative singular case.

You can tell because:

It’s the subject of the sentence – the one performing the action улыбается.
Its dictionary form is also ребёнок. For nouns, the nominative singular is usually the form you see in the dictionary.

Other cases would change the form:

Genitive: ребёнка
Dative: ребёнку
Accusative: ребёнка
Instrumental: ребёнком
Prepositional: о ребёнке

Here, as the subject, it stays ребёнок.

Could I say улыбается к маме or улыбается на маму like in English “smile to/at mom”?

No, not in this context. With улыбаться in the meaning “to smile (to someone),” you:

do not use a preposition,
do use the dative case:
улыбаться маме – to smile at/to mom
улыбаться другу – to smile at/to a friend

Улыбаться к маме and улыбаться на маму sound incorrect or unnatural here.

There are some set expressions with на (e.g. улыбаться на все 32 зуба – to smile with all 32 teeth), but for “to smile at someone,” remember: улыбаться + dative without a preposition.

Is the word order fixed? Can I say Ребёнок улыбается маме, довольный or Маме улыбается довольный ребёнок?

Russian word order is flexible, and your examples are possible, but they change emphasis and style:

Довольный ребёнок улыбается маме.
Neutral: focuses on a “content child” as the subject.
Маме улыбается довольный ребёнок.
Emphasizes маме (to mom): It’s mom that the content child is smiling at (e.g. contrasting with someone else).
Ребёнок улыбается маме, довольный.
Sounds more like spoken, slightly poetic or descriptive: “The child is smiling at his mom, (being) content.”

For a learner, Довольный ребёнок улыбается маме is the most straightforward and neutral version to use.

How is the sentence stressed and pronounced?

Approximate syllable stresses (stressed syllables in caps):

Довольный – доВО́льный: da-VOL-nyi (stress on -во́ль-)
ребёнок – реБЁ́нок: re-BYO-nok (stress on -бён-; ё is always stressed and sounds like yo)
улыбается – улыБА́ется: u-ly-BA-ye-tsa (stress on -ба́-)
маме – МА́ме: MA-me (stress on ма-)

So the rhythm is roughly:

доВО́льный реБЁ́нок улыБА́ется МА́ме.