La muziko estas tro laŭta por la dormanta infano.

Because la means the, and Esperanto uses it wherever English would use the.

• La muziko = the music
• la dormanta infano = the sleeping child

Unlike English, Esperanto has only one definite article: la. It does not change for gender, number, or case.

In Esperanto, nouns end in -o.

So:

• muziko = music
• infano = child

This is one of the most important regular patterns in Esperanto:

• -o = noun
• -a = adjective
• -e = adverb
• -i = infinitive verb

Because laŭta is an adjective describing muziko.

• laŭta = loud
• laŭte = loudly

In the sentence, the word is part of estas tro laŭta = is too loud, so it describes what the music is like. That requires the adjective form -a.

Compare:

• La muziko estas laŭta. = The music is loud.
• La muziko sonas laŭte. = The music sounds loudly.
  This second type is much less natural in meaning; usually you want the adjective in this kind of sentence.

Because in Esperanto, adjectives used after esti still agree with the noun they describe.

So:

• La muziko estas laŭta.
• muziko is a noun
• laŭta describes that noun

This works much like English The music is loud, except Esperanto shows the adjective ending clearly with -a.

If the noun were plural, the adjective would also become plural:

• La kantoj estas laŭtaj. = The songs are loud.

Tro means too, in the sense of more than is desirable.

So:

• tro laŭta = too loud

This is different from:

• tre laŭta = very loud

That distinction is important:

• tre = very
• tro = too much / excessively

This is the Esperanto way to express too ... for ....

• tro laŭta por la dormanta infano = too loud for the sleeping child

Here, por means for. Together with tro, it gives the idea that the loudness is excessive in relation to the child.

So the pattern is:

• tro + adjective/adverb + por + noun

Examples:

• Tro peza por mi. = Too heavy for me.
• Tro malfacila por infano. = Too difficult for a child.

Dormanta is the active present participle, meaning sleeping.

It comes from:

• dormi = to sleep
• dormanta = sleeping, in the state of sleeping

So:

• la dormanta infano = the sleeping child

Why not the others?

• dormi is a verb infinitive: to sleep
• dorma would mean something more like sleep-related or sleepy/sleep-associated, not specifically currently sleeping
• dormanta clearly means the child is sleeping right now

-ant- is the present active participle ending.

It means doing the action right now or in an ongoing way.

So:

• dormi = to sleep
• dormant-a = sleeping

A very useful pattern is:

• -ant- = active, present → doing
• -int- = active, past → having done
• -ont- = active, future → about to do

Examples:

• parolanta homo = a speaking person
• veninta gasto = a guest who came / who has arrived
• forironta trajno = a train about to leave

Because there is no direct object here.

In Esperanto, -n usually marks the direct object. But this sentence is built with estas (is), which links the subject to a description.

Structure:

• La muziko = subject
• estas tro laŭta = predicate
• por la dormanta infano = prepositional phrase

Also, after a preposition like por, you normally do not use -n just because of the preposition.

So:

• por la dormanta infano is correct
• not por la dormantan infanon

Yes. In Esperanto, adjectives agree with the nouns they describe in number and case.

Here:

• dormanta describes infano
• both are singular
• neither has -n

So they match:

• dormanta infano

If plural:

• la dormantaj infanoj = the sleeping children

If accusative:

• Mi vidas la dormantan infanon. = I see the sleeping child.

Yes, that is possible, but la dormanta infano is more natural here.

Esperanto allows fairly flexible word order inside noun phrases, especially in literary or stylistic use. But putting the adjective before the noun is the most straightforward and common choice in a simple sentence like this.

So:

• la dormanta infano = the normal, expected wording
• la infano dormanta = possible, but more marked or stylistic

Yes. Muziko is grammatically a singular noun in Esperanto.

That is normal. Esperanto often uses a regular singular noun where English uses an uncountable noun:

• muziko = music
• akvo = water
• mono = money

So La muziko estas tro laŭta is perfectly normal.

Not exactly.

• tro laŭta = too loud
• tre laŭta = very loud

If you say tre laŭta, you are only saying the music is very loud.
If you say tro laŭta, you are saying it is excessively loud, especially in relation to the sleeping child.

So in this sentence, tro is important because it expresses the idea of more loud than is acceptable for that child.