Broken bento box

Yiu Yiu came back from kindy on Monday with this.

Here’s the conversation that took place:
Mummy: What happened to the box?
Yiu Yiu: I don’t know.
Mummy: You don’t know? What do you mean you don’t know?
Yiu Yiu: It’s spoilt already lar…
Mummy: Who spoiled it?
Yiu Yiu: Nobody, it spoiled by himself (itself) one!
Mummy: Spoilt already so how, cannot use already lor.
Yiu Yiu: Use the other one lar, the bigger one.

Mummy: (So you say pengsan or not?)