Watoto wanapenda zabibu, lakini papai bado ni bichi.

A useful word-by-word breakdown is:

• Watoto = children
• wana-penda = they like
  
  • wa- = they
  • -na- = present tense
  • -penda = like / love
• zabibu = grapes
• lakini = but
• papai = papaya
• bado = still
• ni = is
• bichi = unripe / raw / fresh

So the structure is very close to English: Children like grapes, but the papaya is still unripe.

In Swahili, the verb often includes information that English expresses with separate words.

So wanapenda contains:

• wa- = subject marker, meaning they
• -na- = present tense marker
• penda = verb root, like

That means Swahili does not need a separate word for they here.
English: they like
Swahili: wanapenda

This is because Swahili uses noun class agreement.

• watoto is a plural noun for people, in the wa-/m- human noun classes
• the verb must agree with that noun
• so the verb takes the plural human subject marker wa-

That is why you get:

• watoto = children
• wa-na-penda = they like

The repeated wa- is normal and important in Swahili grammar.

The singular is mtoto, meaning child.

So:

• mtoto = child
• watoto = children

This is a very common singular/plural pair in Swahili:

• singular human: often m-
• plural human: often wa-

It can mean either, depending on context.

• napenda chai = I like tea
• nakupenda = I love you / I like you

In your sentence, wanapenda zabibu, the natural meaning is they like grapes, not a strong romantic love.

Swahili does not have articles like English the, a, or an.

So:

• watoto can mean children or the children
• papai can mean a papaya or the papaya
• zabibu can mean grapes or the grapes

The exact meaning comes from context.

Because the two clauses are built differently.

In watoto wanapenda zabibu, the main verb is wanapenda = like.
That verb already carries the meaning of the action.

In papai bado ni bichi, the sentence is describing a state:

• papai = papaya
• ni = is
• bichi = unripe

So ni works like the English verb to be here.

Bado means still.

It shows that a situation continues up to now.

So papai bado ni bichi means:

• the papaya is still unripe
• it has not become ripe yet

This word is very common in Swahili.

Here bichi means unripe.

More generally, bichi can mean:

• raw
• fresh
• uncooked
• unripe

The exact meaning depends on the noun. With fruit, the usual meaning is unripe.
So with papai, bichi is best understood as unripe.

Swahili adjectives do agree with noun classes, but the form is not always obvious to English learners.

With papai, the adjective bichi appears in a normal form here. In other words, even if you are expecting a very visible prefix on every adjective, Swahili does not always work that way in a simple, predictable English-like pattern.

The important thing for a learner is:

• papai ni bichi = the papaya is unripe
• this is a natural and correct way to say it

Not every Swahili noun shows singular and plural as clearly as mtoto / watoto.

Zabibu is commonly used for grapes without changing form in the way English learners might expect. In everyday use, it often behaves like a fixed noun form.

So you should simply learn:

• zabibu = grapes

This is normal Swahili vocabulary, not a mistake.

Yes, very much so.

The sentence follows a familiar pattern:

• Watoto = subject
• wanapenda = verb
• zabibu = object

Then the second clause:

• lakini = but
• papai = subject
• bado ni bichi = is still unripe

So the overall order is close to: Subject + Verb + Object, but Subject + is + Adjective

That makes this sentence a nice beginner-friendly example.