En cuanto encendimos la calefacción, mi hija se puso a leer junto al radiador con una manta.

En cuanto means as soon as or the moment.

In this sentence, it introduces the action that happened immediately after something else:

• En cuanto encendimos la calefacción...
• As soon as we turned on the heating...

It is a very common time expression in Spanish.

A few similar expressions are:

• tan pronto como = as soon as
• apenas = as soon as / hardly had
• nada más = as soon as

The verb encender means to turn on, to switch on, or to light.

So encendimos la calefacción literally means we switched on the heating.

In Spain, this is perfectly natural for talking about starting the heating system. You may also hear:

• pusimos la calefacción = we put the heating on / turned the heating on

But encender la calefacción is completely standard and clear.

La calefacción means the heating or the heating system in general.

That is different from el radiador, which is just the radiator itself.

So in the sentence:

• encendimos la calefacción = we turned on the heating system
• junto al radiador = next to the radiator

Also, calefacción is feminine, so it takes la.

Both are in the preterite because the sentence describes a sequence of completed past actions:

1. we turned on the heating
2. she started reading

The preterite is very natural here because the speaker is presenting both actions as specific events.

Compare:

• En cuanto encendimos la calefacción, mi hija se puso a leer... = one specific occasion in the past

If this were a repeated habit in the past, Spanish could use the imperfect:

• En cuanto encendíamos la calefacción, mi hija se ponía a leer... = whenever we turned on the heating, she would start reading

Ponerse a + infinitive means to start doing something or to begin doing something, often with a sense of suddenness.

So:

• se puso a leer = she started reading

It is very common in everyday Spanish.

Other examples:

• se puso a llorar = she started crying
• se puso a reír = she started laughing
• me puse a estudiar = I started studying

Compared with empezó a leer, se puso a leer can sound a little more vivid or immediate.

Because this is the pronominal expression ponerse a + infinitive.

Here, ponerse is part of a fixed verbal structure meaning to start doing something. The se does not literally mean herself in English.

So you should learn it as a chunk:

• ponerse a leer = to start reading
• ponerse a trabajar = to start working
• ponerse a hablar = to start talking

Conjugated, it changes with the subject:

• me puse a leer
• te pusiste a leer
• se puso a leer

Because leer can be used on its own to mean to read in a general sense.

So se puso a leer simply means she started reading. It does not need a direct object like un libro.

English works similarly: you can say She started reading without specifying what.

If you wanted to specify it, you could say:

• se puso a leer un libro = she started reading a book
• se puso a leer una novela = she started reading a novel

Junto a means next to, beside, or by.

So:

• junto al radiador = next to the radiator

The form al is the contraction of:

• a + el = al

Since radiador is masculine singular and takes el, Spanish contracts it:

• junto a + el radiador → junto al radiador

This contraction is required.

A similar alternative would be:

• al lado del radiador = next to the radiator

It most naturally means she was with a blanket around her / over her / using a blanket.

Spanish often leaves this slightly less explicit than English. The listener understands the likely situation from context: she is sitting by the radiator and reading, wrapped in a blanket.

So con una manta is broad and natural.

If you wanted to be more explicit, you could say:

• tapada con una manta = covered with a blanket
• con una manta encima = with a blanket over her

Yes. Mi hija empezó a leer is grammatically correct and natural.

The difference is mostly in nuance:

• empezó a leer = neutral, simply states that she began reading
• se puso a leer = often feels a bit more dynamic, as if she just settled down and started reading

So both work, but se puso a leer paints the scene a little more vividly.

Yes. Spanish allows some flexibility in word order.

For example, you could also say:

• Mi hija se puso a leer junto al radiador con una manta en cuanto encendimos la calefacción.

This means essentially the same thing.

The original version puts En cuanto encendimos la calefacción first to emphasize the time relationship: the heating came on, and immediately after that, she started reading.

That fronted clause helps set the scene very naturally.