La petite finit son biberon, puis elle s’endort dans son berceau.

La petite literally means the little one. In context, it usually refers to the little girl or the baby girl.

French often uses an adjective like this as a noun when the meaning is clear from context. So instead of saying la petite fille, French can simply say la petite.

It is feminine because the person being referred to is female.

Because it refers to a feminine person.

In French, adjectives must agree with the noun they describe:

• petit = masculine singular
• petite = feminine singular

Since la petite refers to a girl or female baby, the feminine form petite is used.

Finit is the third-person singular present tense of finir = to finish.

So:

• je finis = I finish
• tu finis = you finish
• il/elle finit = he/she finishes

In this sentence, la petite is the subject, so French uses finit.

Un biberon means a baby bottle or feeding bottle.

So son biberon means her bottle in the sense of the bottle she is drinking from.

It is a masculine noun:

• un biberon
• le biberon

That matters for the possessive adjective used before it.

Because biberon is masculine.

French possessive adjectives agree with the gender and number of the noun possessed, not with the owner.

So:

• son biberon = her bottle / his bottle
• sa bouteille = her bottle / his bottle

Even though the baby is female, French still says son biberon because biberon is masculine.

Puis means then or after that.

It shows sequence:

• first she finishes her bottle,
• then she falls asleep.

Et just means and, while puis more clearly suggests that one action happens after the other.

So in this sentence, puis is a natural choice because it tells the story step by step.

Because s’endormir is the verb meaning to fall asleep.

This is a pronominal/reflexive verb:

• s’endormir = to fall asleep
• endormir without se usually means to put someone to sleep

Compare:

• Elle s’endort. = She falls asleep.
• Elle endort le bébé. = She puts the baby to sleep.

So the s’ is essential here.

The full form is se endort, but French does not normally keep e before another vowel.

So se becomes s’ before endort:

• se + endort → s’endort

This is called elision. You see it often in French:

• je aime → j’aime
• le arbre → l’arbre
• se endormir → s’endormir

S’endort is the third-person singular present tense of s’endormir.

The verb is irregular, so it does not follow a simple pattern like finir.

Here are a few forms:

• je m’endors = I fall asleep
• tu t’endors = you fall asleep
• il/elle s’endort = he/she falls asleep

So elle s’endort means she falls asleep.

Un berceau means a cradle or a bassinet. In many contexts, crib may also fit depending on the translation style.

It is a masculine noun:

• un berceau
• son berceau = her cradle / crib

So dans son berceau means in her cradle/crib.

Because dans means in/inside, which fits the idea of a baby sleeping in a cradle or crib.

• dans son berceau = in her cradle
• sur son berceau would mean on her cradle, which does not make sense here
• au berceau is not the normal way to say physical location in this context

So dans is the natural preposition.

French often uses the present tense to describe actions in a vivid, story-like way, especially in simple descriptions and narration.

So:

• La petite finit son biberon = The little one finishes her bottle
• puis elle s’endort = then she falls asleep

In English, you might also say this in the present when narrating a scene. It makes the action feel immediate.

A simple pronunciation guide would be:

La petite finit son biberon, puis elle s’endort dans son berceau.

Approximate English-style pronunciation: la puh-teet fee-nee son bee-buh-ron, pwee el son-dor dahn son ber-so

A few useful notes:

• petite: the t is pronounced
• puis sounds roughly like pwee
• s’endort has a nasal-like sound in en
• dans also has a nasal vowel
• the final -eau in berceau sounds like oh

This is only an approximation, but it can help you get started.