Дети смотрят на ёлку на площади.

Дети means children. It is the plural form of ребёнок (child).

This is a very common irregular pair:

• ребёнок = child
• дети = children

So you cannot make the plural just by applying a normal ending to ребёнок.

Because the subject дети is plural, the verb must also be in the 3rd person plural form.

The verb is смотреть = to look / to watch.

Its present-tense forms are:

• я смотрю
• ты смотришь
• он / она смотрит
• мы смотрим
• вы смотрите
• они смотрят

Since дети is equivalent to они (they), you use смотрят.

In Russian, смотреть normally takes the preposition на when you mean look at something.

So:

• смотреть на кого? что? = to look at someone/something

Examples:

• смотреть на небо = to look at the sky
• смотреть на дом = to look at the house
• смотреть на ёлку = to look at the Christmas tree / fir tree

This is just the standard pattern of the verb, so it is best learned as a unit: смотреть на + accusative.

Because after смотреть на, Russian uses the accusative case.

The dictionary form is:

• ёлка = fir tree / Christmas tree

But here it changes to the accusative singular:

• ёлку

This happens because ёлка is a feminine noun ending in -а:

• nominative: ёлка
• accusative: ёлку

So:

• Дети смотрят на ёлку. = The children are looking at the tree.

Because here на площади means in the square / on the square as a location, not motion toward it.

With на, Russian often distinguishes:

• куда? (where to?) → accusative
• где? (where?) → prepositional

So:

• на площадь = onto / to the square
• на площади = on / in the square

In this sentence, the square is the place where the scene is happening, so Russian uses the prepositional case:

• площадь → на площади

Because the two на phrases do different jobs.

1. смотрят на ёлку
   Here на belongs to the verb pattern смотреть на = to look at

2. на площади
   Here на shows location = in/on the square

So even though the same preposition appears twice, the grammar is different:

• first на = part of look at
• second на = place

Literally, ёлка means fir tree.

But in everyday Russian, ёлка very often means a Christmas tree or New Year tree, especially in a public setting like a square.

So in this sentence, many learners would naturally understand it as:

• The children are looking at the Christmas tree in the square.

The exact interpretation depends on context, but in modern usage that is very likely.

Ё is a separate Russian letter, pronounced roughly like yo.

So:

• ёлка is pronounced approximately YOL-ka

In many printed texts, Russians often write е instead of ё, so you may see елка. But the correct spelling is ёлка, and for learners it is very helpful to keep ё because it shows the real pronunciation.

So:

• ёлка = correct spelling
• елка = common simplified spelling in everyday print

Russian does not have articles like English a, an, and the.

So Дети смотрят на ёлку на площади could be translated depending on context as:

• The children are looking at the tree in the square
• Children are looking at a tree in the square
• The children are looking at a Christmas tree in the square

English requires an article, but Russian does not. Context tells you whether the meaning is definite or indefinite.

Yes. Russian word order is fairly flexible, although the basic neutral order here is very natural:

• Дети смотрят на ёлку на площади.

You could also say:

• На площади дети смотрят на ёлку.
• На ёлку дети смотрят на площади.

These versions change the emphasis more than the core meaning.

For example:

• На площади дети смотрят на ёлку. emphasizes where this is happening.
• Дети смотрят на ёлку на площади. sounds like a neutral statement.

So the original sentence is a normal, straightforward way to say it.

This is a very common question.

• смотреть = to look, to watch
  This focuses on the action of directing your eyes somewhere.
• видеть = to see
  This focuses on perception or the result of vision.

So:

• Дети смотрят на ёлку. = The children are looking at the tree.
• Дети видят ёлку. = The children see the tree.

In your sentence, the idea is that the children are actively looking at it, so смотрят на is the correct choice.