Das Bügeleisen ist noch warm, deshalb lege ich es nicht neben die Kinder.

Because Bügeleisen is a neuter noun in German, so its basic article is das.

• das Bügeleisen = the iron
• ein Bügeleisen = an iron

German nouns have grammatical gender, and this does not always match anything logical in English, so it usually has to be learned together with the noun.

A good habit is to memorize new nouns as a full unit:

• das Bügeleisen
• not just Bügeleisen

Es refers back to das Bügeleisen.

Since Bügeleisen is neuter, the matching pronoun is es:

• das Bügeleisen → es
• der Tisch → er
• die Lampe → sie

So in deshalb lege ich es nicht ..., es means it.

Here noch means still.

So:

• Das Bügeleisen ist noch warm = The iron is still warm

This is a very common use of noch. It often shows that a condition continues.

Compare:

• Es ist noch warm. = It is still warm.
• Bist du noch hier? = Are you still here?

Because deshalb takes up the first position in the clause, and in a normal German main clause, the finite verb must be in second position.

So the structure is:

• Deshalb = position 1
• lege = position 2
• ich comes after the verb

That is why German says:

• Deshalb lege ich es nicht ...

and not:

• Deshalb ich lege es nicht ...

This is a very important word-order rule in German.

Both can express a reason, but they work differently.

deshalb

Deshalb means therefore / that’s why / for that reason.
It starts a main clause, so the verb stays in second position:

• Das Bügeleisen ist noch warm, deshalb lege ich es nicht neben die Kinder.

weil

Weil means because.
It introduces a subordinate clause, so the verb goes to the end:

• Ich lege es nicht neben die Kinder, weil das Bügeleisen noch warm ist.

So the meaning is similar, but the grammar is different.

Legen means to lay / to put something down.

It is used when you place something in a horizontal or resting position.

So here:

• ich lege es ... = I put it / lay it ...

This fits well with Bügeleisen, because you normally lay an iron down somewhere.

A useful comparison:

• legen = lay something down
• stellen = set something upright / stand something somewhere
• setzen = set someone/something into a sitting position

In everyday speech, legen is the natural verb here.

Here nicht is negating the place/action phrase that follows.

• Ich lege es nicht neben die Kinder. = I am not putting it next to the children.

In German, nicht is often placed before the part it is negating, or near the end of the clause if it negates the whole action.

Here it makes sense before neben die Kinder, because that is the location being rejected.

Compare:

• Ich lege es nicht neben die Kinder. = not next to the children
• Ich lege es neben die Kinder nicht. = unnatural in normal German

Because neben is a two-way preposition. That means it can take:

• accusative for direction/movement toward a place
• dative for location/static position

Here, legen implies movement: the iron is being placed somewhere. So German uses the accusative:

• neben die Kinder = to next to the children

If you were describing where something already is, you would use the dative:

• Das Bügeleisen liegt neben den Kindern. = The iron is lying next to the children.

So:

• legen + neben + accusative = placing it there
• liegen + neben + dative = being there

Because many German plural nouns do not change form between nominative and accusative.

Here the article shows the case:

• nominative plural: die Kinder
• accusative plural: die Kinder
• dative plural: den Kindern

So in this sentence, die Kinder is accusative plural because it follows neben in a movement/direction sense.

Not normally with lege, because legen describes movement to a new position, and that usually requires the accusative after a two-way preposition.

So the natural sentence is:

• Ich lege es nicht neben die Kinder.

If you used den Kindern, it would suggest location rather than destination, which does not fit well with legen.

A better contrast is:

• Ich lege es nicht neben die Kinder. = I am not putting it next to the children.
• Es liegt nicht neben den Kindern. = It is not lying next to the children.

Yes, it is natural. It implies a safety reason:

• The iron is still warm, so I’m not putting it next to the children.

The sentence sounds practical and everyday. It suggests that the speaker wants to avoid danger because the iron could still be hot enough to hurt someone.

The sentence has two main clauses joined by a comma:

• Das Bügeleisen ist noch warm
• deshalb lege ich es nicht neben die Kinder

First clause

• Das Bügeleisen = subject
• ist = verb
• noch warm = predicate/adjective phrase

Second clause

• deshalb = first position
• lege = finite verb in second position
• ich = subject
• es = object
• nicht = negation
• neben die Kinder = directional prepositional phrase

So a rough structure is:

• [Subject] [Verb] ... , [Reason adverb] [Verb] [Subject] ...

This is a very common German pattern.