Sorry, this turned into a thesis. But it's a good read I guarantee it.
First, You have to define how one acquires Undertale's LV, or LOVE (Level Of ViolencE). It's acquired by gaining EXP (EXecution Points). We do know that EXP is not the same as experience points in a traditional 'RPG' sense. When the protagonist of Undertale kills Napstablook, they lose 1 experience point. However, this does not change the EXP count.
Now we have to determine if Sora, Donald, or Goofy could have obtained any EXP. EXP is acquired by killing 'Monsters', and the definition of 'Monster' is less defined. However, there are some key characteristics.
(For all intents and purposes, I will consider Souls equivalent to Hearts, as they essentially function the same way, and are defined the same way. )
1. A monster's body and soul are so closely linked that they cannot exist without the other. This is evident with Flowey, as he is not classified as a Monster in Undertale, and is the only known entity to also not have a soul in Undertale (that I'm aware of).
2. Monsters are not inherently evil. It's eluded to, in the library, that what separates a human soul from a monster soul is that a monster soul requires Love, Hope, and Compassion, where humans do not need this attributes in their soul. Infact, seeing evil in a monster is so rare, that when the protagonist faces off against Asriel Dreemurr, likely the most evil monster, he is quickly persuaded that he is, infact, good. (There is potential that Gaster is an evil monster, but there's so little information about him, that we cannot draw a conclusion. He may not even be a monster.)
3. Monsters are far weaker than humans, unless they consume a human Soul. This is, in part, due to humans having determination. Monsters infused with determination lose their forms and melt. There is one record of a monster using their own determination, which is Undyne. however, even in that case, she started loosing her form, and still lost to a human child.
There are likely more, but this will suffice. Let's go through these one at a time.
1. Since Monsters cannot exist without both a soul and a body, All Heartless and Nobodies do not qualify.
2. Since Monsters are not inherently evil, this also rules out Heartless and Nobodies, as well as Unversed. Although you could argue that not all heartless and nobodies are not inherently Evil, they still do not possess both a body and a soul.
3. This is possibly one rule in favor of, however, only heartless get stronger, and a heartless is nothing without a human heart.
Sora, Donald, and Goofy have only gained experience from defeating heartless, nobodies, and acquiring tech points, with few exceptions. There are a few Disney villains, as well as Master Xehanort, that he Sora has 'vanquished'. However, these are Humans, and humans killing humans is not a valid method of acquiring EXtermination Points.
So that rules out just about everything. Except...
Kingdom Hearts. Specifically, the Kingdom Hearts of the hearts of people in Kingdom Hearts 2. Yeah, this sounds crazy, but hear me out. First, let's go over the first 3 criteria.
1. Kingdom hearts is considered an aggregate of hearts. It therefore both contains a heart, and is a body of hearts.
2. Kingdom Hearts is not inherently Evil. It's even believed that it is the source of light.
3. Kingdom hearts is far weaker than humans. Okay, it's not. Unless you consider than it takes a human to use its power. It therefore is weaker than the human applying its determination on it.
There is a type of Monster called a Boss Monster. The same characteristics above apply, with a few additional characteristics.
4. Boss Monsters' souls persist briefly after death.
5. Boss Monsters only age when their offspring does.
If we follow the events at the end of Kingdom Hearts 2, when Ansem the Wise blows up that Kingdom Hearts, It persists briefly after he kills it. And, only 1 Kingdom Hearts is ever apparent at a time. This possibly implies that as one Kingdom hearts grows, the others fade.
So! Kingdom Hearts can qualify as a Boss Monster. Now what? Well, Neither Sora, Donald, nor Goofy killed Kingdom Hearts.
...But Ansem the Wise did. So he'd likely have an ABSURDLY high Level Of ViolencE.
TLDR; Sora, Donald and Goofy would not have EXP, but Ansem the Wise would (could).