Dokter menempelkan termometer di dahi anak itu sebelum memeriksa suhu tubuhnya.

The root tempel is about sticking or attaching.
Menempelkan means to attach/place something onto something else.

In this sentence, the doctor is doing an action to an object, termometer, and putting it onto a location, di dahi anak itu. That is why menempelkan fits well.

By contrast, menempel is often more like:

• to stick
• to be attached
• to press oneself against something

So menempelkan termometer = attach/place the thermometer, which is the intended meaning here.

Here, -kan helps make the verb mean to cause something to be attached/placed onto a target.

A useful way to think of it is:

• tempel = stick/attach
• menempelkan X di Y = attach/place X onto Y

So in this sentence:

• termometer = the thing being placed
• di dahi anak itu = where it is placed

The exact meaning of -kan can vary from verb to verb, but here it clearly gives the sense of putting something onto something.

Because di marks a location, while ke marks movement toward a destination.

• di = at, on, in
• ke = to, toward

Indonesian normally says menempelkan termometer di dahi because the focus is on the place where the thermometer is positioned: on the forehead.

An English speaker may expect to the forehead, but Indonesian usually uses di with this kind of placement.

Indonesian often expresses possession by putting the possessed thing first and the possessor after it.

So:

• dahi anak itu = that child’s forehead
• literally: forehead child that

This pattern is very common:

• buku saya = my book
• rumah dokter itu = that doctor’s house
• tangan anak itu = that child’s hand

So di dahi anak itu means on the forehead of that child.

In normal Indonesian noun phrases, demonstratives like ini and itu usually come after the noun.

So:

• anak itu = that child / the child
• termometer itu = that thermometer

This is standard word order in Indonesian.
So anak itu is the natural form, not itu anak, when you mean that child as a noun phrase.

Indonesian generally does not use articles like English a, an, and the.

So:

• dokter can mean a doctor or the doctor
• termometer can mean a thermometer or the thermometer

Context tells you which one is meant.

The word itu can help make something definite:

• anak itu = that child or the child

So Indonesian relies much more on context than English does for definiteness.

After sebelum, Indonesian can directly use a verb phrase.

So:

• sebelum memeriksa = before checking

There is no need for a word equivalent to English to here.

The subject is understood from context. Since the doctor is the subject of the first clause, it is natural to understand that the doctor is also the one doing memeriksa.

If you want to make the subject explicit, you could say:

• sebelum dokter itu memeriksa suhu tubuhnya
• sebelum ia memeriksa suhu tubuhnya

But it is not necessary.

Suhu tubuhnya literally means his/her body temperature.

Breakdown:

• suhu = temperature
• tubuh = body
• -nya = his/her/their/its, depending on context

So:

• suhu tubuhnya = his/her body temperature

You could say suhunya, and that can also mean his/her temperature, but suhu tubuhnya is more explicit. In a medical sentence, it sounds natural because it makes clear that the doctor is checking the child’s body temperature.

In this sentence, it most naturally refers to the child.

So suhu tubuhnya is understood as the child’s body temperature.

Indonesian often leaves this kind of reference to context. The ending -nya does not show gender, so it can mean:

• his
• her
• their
• sometimes even a more general definite sense, depending on context

Here, logic tells us the doctor is checking the child’s temperature, not the doctor’s own temperature.

Indonesian verbs usually do not change form for past, present, or future the way English verbs do.

So this sentence could mean different things depending on context:

• a past event
• a habitual action
• a general medical procedure

What the sentence itself clearly shows is the sequence:

1. the doctor places the thermometer on the child’s forehead
2. then the doctor checks the body temperature

The word sebelum tells you the order, not the tense.
If you wanted to make time clearer, you could add words like:

• tadi = earlier
• kemarin = yesterday
• biasanya = usually

Yes. Here di is a preposition meaning at/on/in, so it must be written separately:

• di dahi
• di meja
• di rumah

This is different from the passive prefix di-, which is attached directly to a verb:

• diperiksa = checked / examined
• dibuka = opened
• ditulis = written

So the spelling difference matters:

• di dahi = on the forehead
• diperiksa = is checked / examined

That is a very important distinction in Indonesian writing.