If the person we're talking about had a girlfriend, we would use "Elle a une petite amie." And it wouldn't be a problem to make the difference by ear, since they sound different.
Here are the links to practice "un" and "une" :
In this particular case, "petit" and "petite" would sound the same because of the liaison between "petit" and "ami", but if there is no liaison, for example with "petit livre", the second "t" in "petit" is not pronounced, and therefore "petit" would sound differenty from "petite".
The pronunciation of "petite" never changes.
Sometimes in English we talk about "little friends", though. For example, you're greeting a child you know, and there's a younger one hiding behind him/her. We might say, "Who's your little friend?" There's also the famous movie line, "Say hello to my little friend!" Does this just not happen in French?
Technically, "little friend" could be translated as "petit ami", but because of what it means in actual common French, it's likely that it will not.
For your example of the famous line from Scarface, it was translated in the dubbed version as: "Elle va cracher, ma vieille Sandrine" (which is the furthest possible from a literal translation, but the dubbing French industry gets really creative sometimes).
Actually, a more literal translation could use something like "Dites bonjour à ma petite amie" because of the sexual connotation sometimes used in movies regarding men and their weapon. It would never be understood as "little friend" though, but rather as "girlfriend". Translating is never easy ^^.
"(petit) copain / (petite) copine" and "(petit) ami / (petite) amie" are synonyms.
Usually, using the terms without the adjective "petit(e)" means that we're talking about a buddy/mate for "copain/copine" and a real true friend for "ami/amie" (even though the nuance between these terms can vary depending on who's using them).
Adding "petit(e)" to these two words mean that we're talking about a boyfriend/girlfriend, even though we usually don't need it. We can use only the possessive form (mon copain/ ma copine) to indicate that. Everything else is a matter of context.
Not really, even if the French translation "compagnon" may be a synonym of "copain" (but also may not). They don't belong to the same kind of formality.
"companion" = "compagnon" / "compagne"
There are different meanings for those, see here:
Why would you describe her as a "little friend" in English? That sounds unnatural; just call her your son's friend (and it would be obvious that she is little given their age), or maybe even young friend (« une jeune amie »). If you want to emphasize her small size, then say in French « Mon fils a une amie qui est petite » ("My son has a friend who is little").
Thanks for the reply Sean. I think it's an idiom thing. I'm from Brazil, and in portuguese we may, sometimes, refer to a child's friend as "amiguinho" (one single word that means "little friend"). I thought that in French there was a similar word, since "petit ami" has a totally different meaning. I liked your suggestion , "jeune amie" is the closest to what I was looking for, in terms of meaning.