Meze de la placo staras arbo, kaj infanoj kuras ĉirkaŭ ĝi.

Literally, meze means in the middle or centrally, and de la placo means of the square.

So meze de la placo is the normal Esperanto way to say in the middle of the square.

A very similar alternative is en la mezo de la placo. Both are correct.

• meze de is a bit more compact.
• en la mezo de is a bit more explicitly noun-based, because mezo is a noun meaning middle.

Because placo is not a direct object here.

In meze de la placo, the noun placo comes after the preposition de, and prepositions normally take the basic form, not the -n form.

So:

• la placo = the square
• de la placo = of the square

The -n ending is mainly used for:

• direct objects
• direction in certain expressions

Neither of those applies to placo here.

Because Esperanto word order is flexible.

The sentence begins with the location phrase Meze de la placo, and then puts the verb before the subject: staras arbo. This is a very natural way to present a scene.

It feels similar to English literary word order:

• In the middle of the square stands a tree.

You could also say:

• Meze de la placo arbo staras.
• Arbo staras meze de la placo.

But Meze de la placo staras arbo sounds especially natural when you are first describing what is in that place.

In Esperanto, stari is commonly used for things that are upright and in a fixed position.

So a tree, a bottle, a tower, or a person can all stari if they are upright.

Here, staras arbo means something like:

• a tree stands
• there is a tree standing
• a tree is standing there

Using staras is more vivid than just saying estas.
Compare:

• Meze de la placo estas arbo = There is a tree in the middle of the square.
• Meze de la placo staras arbo = In the middle of the square stands a tree.

Because arbo is being introduced as a new thing in the scene, so it is indefinite: a tree, not the tree.

Esperanto uses la only for definite nouns.

So:

• arbo = a tree / tree
• la arbo = the tree

In this sentence, the listener has not been told about this tree before, so arbo is the natural choice.

For the same basic reason: the sentence is just mentioning some children in the scene, not a specific previously identified group.

So:

• infanoj kuras = children are running / some children run
• la infanoj kuras = the children are running

If you said la infanoj, it would sound as if the listener already knows which children you mean.

ĉirkaŭ ĝi means around it.

The pronoun ĝi is used because it refers back to arbo, and a tree is a non-person noun. In Esperanto, ĝi is the normal pronoun for things and for animals when no sex is being specified.

So:

• arbo → ĝi
• ĉirkaŭ ĝi = around it

English speakers sometimes hesitate because English often avoids it for living things, but in Esperanto ĝi is completely normal for a tree.

Yes, absolutely.

Both are correct:

• infanoj kuras ĉirkaŭ ĝi = children run around it
• infanoj kuras ĉirkaŭ la arbo = children run around the tree

Using ĝi simply avoids repeating arbo.

Because Esperanto does not add -n to every phrase involving movement.

The directional -n is used mainly when you are showing movement toward a place:

• en la domon = into the house
• sur la tablon = onto the table

But ĉirkaŭ ĝi means around it, not toward it. The children are moving in a circle around the tree, so the ordinary prepositional phrase is enough.

So kuras ĉirkaŭ ĝi is the normal form.

Yes.

meze is the adverb form related to meza (middle, central) and mezo (middle, as a noun).

In meze de la placo, it functions adverbially in a fixed expression meaning in the middle of.

Related forms:

• meza = middle, central
• mezo = the middle
• meze = in the middle / centrally

So this sentence is using a very common pattern: meze de + noun.

A rough guide for an English speaker is:

• ĉ sounds like ch in church
• ĝ sounds like j in jam
• ŭ is a short glide, like the w-part in English cow

So:

• ĉirkaŭ is roughly CHEER-kow, with the stress on ĉir
• ĝi is roughly jee, with a soft j sound

Also remember that Esperanto stress is always on the second-to-last syllable:

• ME-ze
• PLA-co
• STA-ras
• IN-fa-noj
• ĈIR-kaŭ