Mama aliuliza watoto walipo jana usiku.

A simple breakdown is:

• Mama = mother / mum
• aliuliza = asked
• watoto = children
• walipo = where they were
• jana usiku = last night

So the sentence structure is a little different from English, but those are the main pieces.

aliuliza comes from the verb kuuliza, meaning to ask.

It breaks down like this:

• a- = he/she
• -li- = past tense
• -uliza = ask

So aliuliza means he/she asked.
Because Mama is a singular human noun, Swahili uses the a- subject marker.

Because watoto is plural and refers to people.

In Swahili, verbs agree with the noun class of the subject. For plural people, the subject marker is wa-.

So:

• watoto walipo = the children where-they-were
• mtoto alipo = the child where-he/she-was

That wa- is the agreement marker for they.

Here walipo means where they were.

A helpful way to think of it is:

• wa- = they
• -li- = past
• -po = a locative element connected with place

So instead of using a separate word for where, Swahili often builds the idea of location into the verb form itself.

In this sentence, walipo is the part that gives the meaning where the children were.

Because this sentence uses an indirect question.

In a direct question, you would normally use wapi, for example:

• Watoto walikuwa wapi jana usiku? = Where were the children last night?

But after a verb like aliuliza (asked), Swahili often uses forms like:

• alipo = where he/she was
• walipo = where they were
• tulipo = where we were

So walipo is a very normal way to say where they were in an embedded or indirect question.

Because Swahili does not structure this kind of clause the same way English does.

English says:

• where the children were

Swahili keeps watoto as the subject and then uses walipo as the verb form carrying the idea of location:

• watoto walipo

So the sentence is not following English word order. The meaning of where is inside walipo, rather than being a separate fronted word.

In this sentence, the natural reading is:

• Mother asked where the children were last night.

Here watoto belongs with walipo and functions as the subject of the embedded clause.

If you want to say Mother asked the children where they were last night, Swahili would usually make that clearer, for example with an object marker:

• Mama aliwauliza watoto walikuwa wapi jana usiku.

The -wa- in aliwauliza helps show that the children are the ones being asked.

jana usiku means last night.

Literally, it is something like yesterday night, but the natural English translation is last night.

This is a very common time expression in Swahili.

Because time expressions often come near the end of the clause in Swahili.

So:

• Mama aliuliza watoto walipo jana usiku

is a natural way to say it.

You can sometimes move time expressions for emphasis, but the end position is very normal and common.

Swahili does not use articles like English the or a/an.

So:

• Mama can mean mother, the mother, or mum, depending on context.
• watoto can mean children or the children, depending on context.

The listener understands definiteness from the situation rather than from a separate article.

Yes, that would be understandable, and many learners first meet where questions in that pattern.

But there is a difference in style:

• watoto walikuwa wapi = more like a straightforward where were the children?
• watoto walipo = a compact indirect-question structure meaning where the children were

So the sentence with walipo is teaching you an important Swahili pattern for embedded location questions.