Learn Hardcore Swahili: Watoto wanacheza na kuimba kwa wakati mmoja. - The children are playing and singing at the same time.

wa- = subject prefix for they (plural humans, agreeing with watoto – children)
-na- = present tense / present continuous (roughly are …ing or do in English)
-cheza = verb root cheza (to play)

So wanacheza means they are playing (or they play), and it agrees with watoto both in person and number.

Why is it na kuimba and not na wanaimba?

In Swahili, when two actions share the same subject, it is very common to:

Fully conjugate the first verb: wanacheza
Use na + ku- + verb for the second: na kuimba

So:

Watoto wanacheza na kuimba…
= The children are playing and (also) singing (same children doing both actions).

Putting wanaimba after na would be grammatically possible, but it changes the feel of the sentence (more like two separate full clauses: they are playing and they are singing). The version with na kuimba sounds more like playing while singing / playing and singing together as one combined activity.

Is na here “and” or “with”? I thought na means “with”.

Na in Swahili has several uses:

and: joining words or actions
- watoto na wazazi = children and parents
- wanacheza na kuimba = they are playing and singing
with: indicating accompaniment
- Ninakwenda na rafiki yangu = I am going with my friend

In wanacheza na kuimba, na is working as and, linking two actions done by the same subject.

Can I say Watoto wanacheza na wanaimba kwa wakati mmoja instead? Is that wrong?

It is not wrong; it is grammatically fine:

Watoto wanacheza na wanaimba kwa wakati mmoja.
= The children are playing and are singing at the same time.

However, there is a nuance:

wanacheza na kuimba: sounds like a single combined activity – playing while singing.
wanacheza na wanaimba: feels more like two parallel actions that both happen, but less tightly fused as one activity.

Both are understandable; the original sentence sounds a bit more natural and smoother in everyday Swahili.

What exactly does kwa wakati mmoja mean? How is it built?

Kwa wakati mmoja is a set phrase meaning at the same time / simultaneously.

Breakdown:

kwa = by / with / at (a general preposition used in many expressions)
wakati = time (as a noun)
mmoja = one

Literally: by/at one time → idiomatically: at the same time.

So the whole sentence says that the children are doing both activities simultaneously.

What does kwa add in kwa wakati mmoja? Could I just say wakati mmoja?

Kwa is a preposition here that:

Links the noun wakati to the rest of the sentence.
Makes the phrase sound natural and idiomatic.

You could say:

Watoto wanacheza na kuimba wakati mmoja.

People will understand you, but it sounds a bit off or less natural. The usual and most idiomatic expression is kwa wakati mmoja in this context, just like fixed prepositions in English (at the same time, not in the same time).

Does wakati mmoja literally mean “one time”? Why does it mean “at the same time”?

Literally, yes:

wakati = time
mmoja = one

So literally: one time.

In usage, wakati mmoja (especially with kwa) has the idiomatic meaning the same time / simultaneously, because you are talking about different actions sharing one common time frame.

This is similar to English where one day can sometimes mean the same day depending on context.

Does wanacheza mean “are playing” (progressive) or “play” (simple present)?

The Swahili present marker -na- covers both:

ongoing actions:
- Watoto wanacheza sasa. = The children are playing now.
general or habitual actions:
- Watoto wanacheza kila siku. = The children play every day.

Context decides whether you translate as are playing or play.
In your sentence, because of kwa wakati mmoja and the feeling of a current scene, English are playing and singing is the most natural translation.

Why is there no word for “the” before watoto? How do I know if it means “children” or “the children”?

Swahili normally has no articles like a, an, the. The noun watoto simply means children.

Context tells you whether to translate it as:

children (children in general)
the children (specific group already known in the conversation)
sometimes some children (an unspecified group)

So the single word watoto can correspond to children / the children / some children, depending on the situation.

How does watoto agree with the verb wanacheza?

Watoto (children) belongs to noun class 1/2 (people):

Singular: mtoto (child) — takes subject prefix a-
Plural: watoto (children) — takes subject prefix wa-

The verb must match the noun class:

Mtoto anacheza. = The child is playing.
- a- = he/she (class 1 singular)
Watoto wanacheza. = The children are playing.
- wa- = they (class 2 plural)

So wa- in wanacheza is agreeing with watoto.

Can I put kwa wakati mmoja somewhere else in the sentence, or must it be at the end?

The most natural position is at or near the end:

Watoto wanacheza na kuimba kwa wakati mmoja. ✅

You can move it earlier, but it starts to sound less natural or more marked:

Kwa wakati mmoja, watoto wanacheza na kuimba.
→ Grammatically okay; sounds like you are emphasizing at the same time (e.g., in written style or storytelling).

Inside the verb phrase, between the verbs, is normally avoided:

✗ Watoto wanacheza kwa wakati mmoja na kuimba. (sounds awkward)

So: end position is best in everyday speech.

Is na kuimba only used with cheza, or can I use this pattern with other verbs?

You can use this structure very broadly. The pattern is:

[Subject]-na-[Verb1] na ku-[Verb2]

Meaning: The subject is doing Verb1 and (also) Verb2 (same subject, same time).

Examples:

Anakula na kuzungumza.
= He/she is eating and talking.
Wanaimba na kucheza.
= They are singing and dancing.
Ninasoma na kuandika.
= I am reading and writing.

So na kuimba is just one example of a very common pattern: conjugated verb + na ku- + second verb sharing the same subject.