Fragen über die Beispielsätze mit, und die Definition und Benutzung von "Muchacho"

A: you posted it in the english section
Niño and Niña
Niño and niña are more general and sometimes slightly more formal words for children. Their use might be preferred in situations where we'd talk about a child in English rather than a boy or girl.

joven is used for young like vino joven

Joven
Joven are the rough equivalents of "youth" (as a noun) and "adolescent" and can refer to young people of either sex. Although the words are often translated as "teenager," their use isn't strictly limited to the ages of 13 to 19.


Muchacho and Muchacha
When referring to adolescents or teenagers, muchacho/a can usually be used interchangeably with chico/a. In most areas it isn't used often when referring to younger children.

Muchacho/a can also be used to refer to a young servant or maid.

Chico and Chica
As a general adjective, chico is simply a word for "small," especially when referring to something that is smaller than other beings or things of its type. When it becomes a noun referring to people, however, it usually refers to someone of a young age rather than someone of short stature. The age of children used for chico and chica varies somewhat with region.
It is also very common to use chica when referring to young, single women, especially those who are of potential romantic or sexual interest—something like the equivalent of "babe." To a lesser extent, chico can fulfill a similar role. Similarly, the two terms commonly are used for "girlfriend" and "boyfriend," respectively.

The main characters in a movie, TV show, or novel are often referred to as chico or chica, especially if they are young and attractive.