Learn Hardcore Swahili: Watoto watakuwa wakicheza mchezo wa bodi sebuleni wakati sisi tunapika. - The children will be playing a board game in the living room while we cook.

Watoto watacheza mchezo wa bodi …
= The children will play a board game…
This is a simple future. It just says the action will happen at some point in the future.
Watoto watakuwa wakicheza mchezo wa bodi …
= The children will be playing a board game…
This describes an action that will be in progress at a particular time in the future (here, while we cook).

So watakuwa wakicheza is like English “will be playing”. It emphasizes the ongoing nature of the action at that future time, not just the fact that it will happen.

What exactly does the prefix waki- in wakicheza mean?

wakicheza breaks down like this:

wa- = subject marker for they (3rd person plural, agreeing with watoto)
-ki- = a marker often glossed as “while / when / as (doing something)”
-cheza = root play

So literally, wakicheza means something like “while they are playing / when they play”.

On its own, wa- + -ki- + verb often introduces a simultaneous or background action:

Wakiimba, walimu waliingia.
While they were singing, the teachers came in.

In your sentence, when you combine watakuwa + wakicheza, it functions like a future progressive:

watakuwa wakicheza
≈ they will be (while-they-are) playing → they will be playing

Is watakuwa wakicheza basically a “future continuous” tense? How would I say things like “I will be reading” or “we will be working”?

Yes, watakuwa wakicheza is the normal Swahili way to express what English calls the future continuous / future progressive.

Pattern:

[subject] + -ta-kuwa + [subject] + -ki- + verb

Examples:

Nitakuwa nikisoma.
I will be reading.
Tutakuwa tukifanya kazi.
We will be working.
Atakuwa akiendesha gari.
He/She will be driving.

Native speakers may sometimes drop the second subject marker (especially in speech), but the fully clear pattern is like in your sentence: watakuwa wakicheza.

Why is it mchezo wa bodi and not something like mchezo ya bodi?

The wa/ya/cha/la… in phrases like this is a possessive/“of” connector that must agree with the head noun, not the following noun.

The head noun is mchezo (game), which is noun class 3/4.
Class 3/4 uses wa for this connector.

So:

mchezo wa bodi
= game of (the) board → board game

We use wa because it agrees with mchezo, not with bodi.

More examples with mchezo:

mchezo wa mpira – ball game / football
mchezo wa karata – card game
mchezo wa kompyuta – computer game

What does bodi mean here, and are there other ways to say “board game” in Swahili?

bodi here is a loanword from English “board”.

mchezo wa bodi is a direct way to say “board game”, especially in more modern / urban speech.

Other possibilities you may see or hear:

mchezo wa ubao – literally game of the board (using ubao = wooden board)
With English influence: gemu/mchezo wa bodi or magemu ya bodi (plural slangy “games”)

Usage varies by region and context, but mchezo wa bodi or mchezo wa ubao are both understandable as “board game” in learner contexts.

What exactly does sebuleni mean, and what does the -ni ending do?

Sebuleni comes from:

sebule = living room
-ni = a common locative suffix meaning in, at, on (depending on context)

So:

sebule – living room (as a thing)
sebuleni – in the living room / at the living room (location)

The -ni suffix is widely used to mark location:

nyumba → nyumbani – house → at home / in the house
darasa → darasani – classroom → in the classroom
kanisa → kanisani – church → in/at church

Could I just say sebule without -ni, or would that change the meaning?

Without -ni, you normally lose the “in/at” sense.

Compare:

Watoto wako sebule.
Sounds more like The children are the living room (ungrammatical/odd), unless context very strongly implies location.
Watoto wako sebuleni.
The children are in the living room.

In Watoto watakuwa … sebuleni, you need -ni to show that sebuleni is the place where the children will be playing. So sebuleni is the natural and correct form here.

Why do we have wakati sisi tunapika instead of just wakati tunapika? Is sisi necessary?

The personal pronoun sisi is not grammatically required. Swahili verbs already show the subject with a prefix:

tunapika = tu- (we) + -na- (present) + pika (cook)

So:

wakati tunapika
= while we cook / while we are cooking
is already clear and correct.

Adding sisi gives emphasis or contrast, something like:

wakati sisi tunapika
≈ while we (for our part) are cooking
→ possibly contrasting us with them (e.g. they will be playing while we are the ones cooking).

In many neutral contexts, speakers would simply say wakati tunapika.

Why is tunapika in the present tense when the main clause is in the future? Could I say wakati sisi tutapika instead?

Swahili often uses a present tense verb in a “wakati…” clause to talk about the future, when the main clause clearly sets a future time.

Here:

Watoto watakuwa wakicheza … wakati sisi tunapika.
Literally: The children will be playing … when/while we cook.
Like English: … while we cook (not while we will cook).

This is very natural.

You can say wakati sisi tutapika, but it changes the feel:

wakati sisi tutapika – when we will cook → focuses more on cooking as a single future event/time point.
For a continuous sense similar to the main clause, you might even hear more complex forms like wakati tutakapokuwa tunapika, but that’s more advanced.

For everyday speech, wakati tunapika with present tense is the simplest and most natural in this sentence.

Can I put the wakati clause at the beginning, like Wakati sisi tunapika, watoto watakuwa wakicheza mchezo wa bodi sebuleni?

Yes. Both orders are correct:

Watoto watakuwa wakicheza mchezo wa bodi sebuleni wakati sisi tunapika.
Wakati sisi tunapika, watoto watakuwa wakicheza mchezo wa bodi sebuleni.

Putting wakati… first just changes the information flow, not the basic meaning. Often a comma is used in writing when the wakati clause comes first.

Again, you can also drop sisi if you don’t need emphasis:

Wakati tunapika, watoto watakuwa wakicheza …

I see wa- in watoto, watakuwa, and wakicheza. Are these all the same wa-, and what do they show?

They are related but play slightly different roles:

watoto
- wa- here is the noun class 2 prefix (plural) for people.
- mtoto (child) → watoto (children).
watakuwa
- wa- is the subject marker agreeing with watoto = they.
- -ta- = future marker
- -kuwa = be
  → watakuwa = they will be.
wakicheza
- wa- again is the subject marker = they
- -ki- = “while/when (doing)”
- -cheza = play
  → wakicheza = while they are playing.

So:

In watoto, wa- marks plural people as a noun.
In watakuwa / wakicheza, wa- marks they as the subject of the verb, agreeing with watoto.

This agreement is what ties the verbs to the noun watoto in the sentence.