Mama me poljubila prije spavanja, a sestra mi je posudila narukvicu umjesto izgubljene naušnice.

Yes — in standard, neutral Croatian, you would normally say Mama me je poljubila prije spavanja.

Croatian past tense is usually made with:

• a present-tense form of biti (sam, si, je, smo, ste, su)
• plus the past participle, here poljubila

So:

• Mama me je poljubila
• Sestra mi je posudila

The version without je in the first clause sounds elliptical or colloquial. A learner should generally include je.

They are both short forms of I/me, but in different cases.

• me = accusative form, used for a direct object
  
  • Mama me je poljubila = Mom kissed me
• mi = dative form, used for an indirect object
  
  • Sestra mi je posudila narukvicu = Sister lent me a bracelet

So the difference is grammatical role:

• me = the person directly affected by the action
• mi = the person something is given/lent to

These are short unstressed words called clitics, and Croatian places them in a special position near the beginning of the clause — usually after the first stressed word or phrase.

So the normal order is:

• Mama me je poljubila
• Sestra mi je posudila narukvicu

For a learner, the safest thing is to remember the whole pattern:

• X me je ...
• X mi je ...

In other words, don’t try to place je wherever you want. Clitic order is fairly fixed.

Because they agree with the subject in gender and number.

Both subjects are feminine singular:

• mama
• sestra

So the past participle is feminine singular:

• poljubila
• posudila

Compare:

• Mama je poljubila = feminine singular
• Tata je poljubio = masculine singular
• Sestre su posudile = feminine plural

This agreement is a very important part of Croatian past tense.

Croatian often leaves out possessives like my when the relationship is obvious from context.

So:

• Mama often naturally means my mom
• Sestra often naturally means my sister

You can say:

• Moja mama
• Moja sestra

but it is not necessary unless you want emphasis, contrast, or extra clarity.

Prije means before, and it is followed by the genitive case.

Here:

• spavanje = sleeping / sleep / bedtime
• genitive singular = spavanja

So:

• prije spavanja = before sleeping / before bedtime

This is a very common Croatian structure:

• prije ručka = before lunch
• prije škole = before school
• prije odlaska = before leaving

Umjesto takes the genitive case.

So:

• naušnica = earring
• genitive singular = naušnice

And the adjective must match:

• izgubljena naušnica = a lost earring
• izgubljene naušnice = of a lost earring / instead of a lost earring

That is why you see:

• umjesto izgubljene naušnice

A useful thing to notice: izgubljene naušnice may look plural to you, but here it is actually genitive singular feminine.

Because it is the direct object of posudila, so it is in the accusative singular.

The noun is:

• nominative: narukvica = bracelet
• accusative: narukvicu

So:

• Sestra mi je posudila narukvicu = Sister lent me a bracelet

This is a regular pattern for many feminine nouns ending in -a:

• knjiga → knjigu
• torba → torbu
• narukvica → narukvicu

It can be confusing, because posuditi can be used in ways that correspond to either lend or borrow in English, depending on the structure and context.

In this sentence:

• Sestra mi je posudila narukvicu

the meaning is clearly:

• My sister lent me a bracelet or
• My sister let me borrow a bracelet

Why? Because:

• mi = to me
• narukvicu = the thing being lent

So the direction of the action is toward me.

A often connects two clauses with a slight contrast, shift, or parallel comparison.

Here:

• Mama me je poljubila..., a sestra mi je posudila...

This sounds like:

• Mom did one thing, and sister did another
• there is a natural contrast or change of subject

If you used i, it would sound more like simple addition:

• Mama me je poljubila i sestra mi je posudila narukvicu

That is not impossible, but a is more natural here because the sentence shifts from mama to sestra.

Because these are perfective verbs, which fit single completed actions.

• poljubiti = to kiss once / give a kiss
• posuditi = to lend/borrow as a completed action

That matches the sentence well:

• one kiss before sleep
• one completed act of lending the bracelet

If you used imperfective verbs like:

• ljubila
• posuđivala

the meaning would suggest something repeated, ongoing, or habitual, which does not fit as well here.

It comes from a verb, but here it behaves like a noun.

• verb: spavati = to sleep
• verbal noun: spavanje = sleeping

Croatian often uses these verbal nouns after prepositions:

• nakon jela = after eating / after the meal
• prije spavanja = before sleeping
• bez razmišljanja = without thinking

So although it comes from a verb, in the sentence it functions like a regular neuter noun.

Yes, absolutely:

• Moja mama me je poljubila prije spavanja, a moja sestra mi je posudila narukvicu umjesto izgubljene naušnice.

That version is grammatical, but it sounds a bit heavier. Croatian often prefers the shorter version when ownership or family relationship is obvious.

So:

• mama, sestra = more natural in many contexts
• moja mama, moja sestra = more explicit or emphatic