Idea
The Pun Tyrant
This is extremely dangerous territory. Has the most potential to go poorly. Makes people wonder about you. Why are you writing from the perspective of an 8-year-old? Are you okay? True Evil because that is the only morally correct placement for playing a child (unless you are also a child, in which case, you are exempt from criticism).
Considering this is a type of character I really like to play, let me give my reasons (and since you asked and all):
----> Cuteness / Wholesomeness
---> An interesting perspective, the simple innocence and lack of understanding
---> Can bring out sides of other characters you don't normally get to see
---> Have built-in obstacles in the form of their lack of knowledge and not being as physically developed
Then there's those types of "children-but-not-really" types which have some dramatic and a lot of comedic potential in my eyes, but that's probably another topic entirely.
I suppose my main disagreement is classifying playing such a character as "evil", in inherent terms anyway. I don't think playing a character that's particularly young is any different morally than playing one that's really old, or playing a character that went to war when you didn't, or basically any other surface-level trait of a character. There's really no reason why it would be outside of assumptions made about the player, but even if we were to presume those assumptions generally true I don't think it would follow that the character archetype itself is an issue.
That being one must acknowledge there is such a thing as people simply being uncomfortable with there being a child within, say, violent situations (the example that comes to mind is in a post-apocalyptic roleplay). Personally I feel the dynamic that can be established and again the presence of that perspective are two things that kind of character can contribute very well to such an RP, but people are uncomfortable with what they are uncomfortable with. So there are times when playing certain types of characters fits better than others, and that goes for child characters as well.