Infans matri osculum dat antequam dormiat.

Here is a quick parse:

• infans — nominative singular; the subject of the sentence
• matri — dative singular of mater, matris; the indirect object
• osculum — accusative singular; the direct object
• dat — 3rd person singular present active indicative of dare; gives
• antequam — conjunction meaning before
• dormiat — 3rd person singular present active subjunctive of dormire; goes to sleep / may go to sleep

So the structure is basically:

subject + indirect object + direct object + verb + before-clause

Because matri is the person to whom something is given.

With dare, Latin normally uses:

• the accusative for the thing given
• the dative for the recipient

So:

• osculum = the thing given
• matri = to the mother

That is why Latin uses matri, not matrem.

Because it is the direct object of dat.

The baby is giving what?
A kiss: osculum

In Latin, the direct object of a verb like dare is regularly in the accusative.

Because Latin does not have articles like English.

So infans can mean:

• the baby
• a baby

and osculum can mean:

• the kiss
• a kiss

Which one sounds best depends on context. Latin usually leaves that for the reader to infer.

Latin word order is much more flexible than English word order because the case endings already show each word’s job.

So all of these could be understood grammatically:

• Infans matri osculum dat
• Infans osculum matri dat
• Matri infans osculum dat

The version you have is very natural Latin. Putting dat near the end is especially common. The order can also create slight emphasis, but the basic meaning stays the same because the endings tell you who is doing what.

Yes. Osculum dare alicui is a perfectly normal Latin expression.

Literally it means to give a kiss to someone, and idiomatically it corresponds to English to kiss someone or to give someone a kiss.

Latin can also use a verb such as osculari, but osculum dare is very common and straightforward.

Because antequam can introduce a clause with the subjunctive when the action is viewed as anticipated or not yet realized from the point of view of the main action.

Here the kiss happens first, and the sleeping is still about to happen:

• the baby gives the mother a kiss
• then the baby goes to sleep

So dormiat presents the sleeping as something still ahead at that moment.

A learner-friendly way to think about it is:

• antequam + indicative often states a more straightforward fact
• antequam + subjunctive often presents the action as expected, intended, or still pending

In some contexts, yes, antequam can be followed by the indicative. But the choice affects the nuance.

• dormit would treat the sleeping more as a plain fact
• dormiat gives it a more prospective feel: the baby gives the kiss before going to sleep

So the subjunctive here is not random; it helps express how the second action is being viewed.

Most naturally, the baby.

Since the main subject is infans, and no new subject is stated in the antequam clause, readers will usually understand the same subject to continue unless context suggests otherwise.

So the default reading is:

• the baby gives the mother a kiss
• before the baby goes to sleep

If Latin wanted to make it clearly the mother who is sleeping, it would usually add something to show that more explicitly.

No, not by itself.

Infans is a noun that can refer to either a male or a female infant. So in English, depending on context, you might translate it as:

• the baby
• the infant
• he
• she

If Latin needed to make the sex clear, it could do so through context, adjectives, or pronouns.

Because mater is a 3rd-declension noun, and its dative singular is formed from the stem matr- plus the ending -i:

• nominative: mater
• genitive: matris
• dative: matri

So matri is simply the regular dative singular form meaning to the mother.