Watoto waligusa nyavu za goli baada ya mazoezi, lakini mwalimu akawaambia wasiingie uwanjani tena.

Because watoto is a plural noun meaning children, and Swahili verbs agree with the subject.

So in wa-li-gusa:

• wa- = they
• -li- = past tense
• -gusa = touch

That wa- matches watoto.

Waligusa = wa-li-gusa

• wa- = they
• -li- = past tense
• -gusa = touch

So it means they touched.

Because nyavu belongs to a noun class that takes the possessive connector za.

So:

• nyavu = nets / netting
• za = of for that noun class
• goli = goal

So nyavu za goli literally means the nets of the goal, which in natural English is often just the goal net or the goal nets.

It breaks down like this:

• baada = after
• ya = of
• mazoezi = exercises / practice / training

So literally it is after of practice, but naturally it means after practice or after training.

Yes, mazoezi is formally a plural-form noun, but in real usage it often means:

• exercise
• practice
• training

This is normal in Swahili. Some activity or abstract nouns look plural even when English uses a singular-style word.

Akawaambia can be broken down as:

• a- = he/she
• -ka- = and then / so / next
• -wa- = them
• -ambia = tell / say to

So mwalimu akawaambia means something like the teacher then told them.

The -ka- form is very common in narration. It links one event to the next.

So here the sequence is:

1. the children touched the nets
2. then the teacher told them something

Using -ka- gives that and then / so feeling.
So akawaambia is not just told them, but more like then told them.

It is inside the verb as -wa-.

So:

• a-ka-wa-ambia
• he then them told

Swahili often puts object pronouns inside the verb, instead of using a separate word like English does.

Wasiingie is a negative subjunctive form.

It breaks down as:

• wa- = they
• -si- = negative
• -ingie = enter / go in

So it means that they should not enter or not to go in.

After verbs like tell, order, ask, or warn, Swahili often uses the subjunctive for what someone is supposed to do or not do.

So mwalimu akawaambia wasiingie means the teacher told them not to go in / not to enter.

Uwanjani comes from uwanja, meaning field, ground, or pitch, plus the locative ending -ni.

So:

• uwanja = field
• uwanjani = in/on/at the field

In this sentence, natural English would be onto the field or on the field, depending on context.

Tena means again.

At the end of the sentence, it gives the sense of:

• not to go onto the field again
• not to go back onto the field anymore

So it strengthens the warning or instruction.

Yes. Even though kuingia literally means to enter/go in, the natural English translation depends on context.

With uwanjani in a sports context, English often says:

• go onto the field
• go on the pitch
• enter the field

All of those can fit, depending on how natural you want the English to sound.