Learn Hardcore Vietnamese: Bé thích cá chiên không ớt. - The child likes fried fish without chili pepper.

Bé usually means a small child, little kid, or baby, depending on context. In this sentence, it most naturally means the child / the little one.

It can also be used:

as a noun: bé = small child
as a way to address a child affectionately
sometimes even as an affectionate way to address a romantic partner, depending on context

Here, the safest reading is simply the child.

Why is there no word for the or a before bé or cá?

Vietnamese does not use articles like the and a/an the way English does.

So:

bé can mean the child, a child, or just child
cá can mean fish in a general sense

You understand whether it is definite or indefinite from context. That is very normal in Vietnamese.

How does thích work in this sentence?

Thích means to like.

The basic pattern is:

Subject + thích + thing/action

So in this sentence:

Bé = the child
thích = likes
cá chiên không ớt = fried fish with no chili

Vietnamese does not need an extra word like to here. It is simply bé thích... = the child likes...