Since the release of Silksong, putting aside the question of whether Lace and Hornet are actually related, the biggest debate among fans has probably been this:
Is Lace actually a child, or is she an "adult forced to play a child"?
I think the answer is the former—Lace is a child.
The reason I believe Lace is a child—or more precisely, that she is not written as an adult in the story—is because if Lace were an "adult who is fully mature on the inside but forced to play an immature child, feeling pained and oppressed by it," then Hornet would become the absolute worst asshole I've seen in recent years.
First, let me clarify that from the perspective of "chronological age," Lace is "an adult," as character dialogue tells us she has lived for a very long time. However, what I am discussing is being a minor "narratively and mentally." A similar example is Aang from Avatar: The Last Airbender. According to the plot, he is technically over 100 years old (having been frozen in ice for a century), but his mentality and the role the story assigns to him still treat him as a teenager, not a 100-year-old grandpa. I believe Lace is given a similar character treatment in Silksong—she is treated as a minor.
Based on the game's content, we can gather three facts that no one would dispute:
Hornet is fundamentally a kind, good person, a hero.
Hornet is deeply aware of Lace's trauma and pain and wishes to help/save her.
Hornet repeatedly uses the word "child" to address or refer to Lace.
Given these three points, if Lace were an adult "forced to play a child and suffering because of it," the premise that "Hornet is a good person" would completely fall apart. This would even make Hornet a massive jerk. Knowingly calling an adult who doesn't want to be treated as a child "child," while being fully aware of their pain, is, in my opinion, just as malicious as intentionally misgendering a transgender person (knowing they suffer from severe gender dysphoria) or calling someone with extreme body anxiety a "fatass." This is not how a hero acts; it's the behavior of the most one-dimensional bullies.
I know that sometimes when two people are exceptionally close, they might use specific terms to address each other—like female friends using derogatory or misogynistic terms as an alternative expression of being "besties." However, in Silksong, Hornet and Lace have clearly known each other for a very short time, and Hornet's personality doesn't seem like the type to do this.
Therefore, if the premise that "Lace is an adult" were true, Hornet constantly calling her "child" would only be a severe insult or continuous psychological torture for Lace; at least, I cannot think of any other well-intentioned interpretation. Furthermore, the final ending scene where Lace and Hornet's weapons rest side-by-side (regardless of whether you interpret their subsequent relationship as relatives, master and apprentice, friends, or lovers) would only symbolize that "another cycle of abuse is about to begin." The Sister of the Void ending would become a bad ending for Lace, and the thematic essence of the story would be heavily corrupted.
By contrast, if we consider Lace a child narratively, Hornet's characterization remains intact, and "child" becomes a relatively objective statement rather than a degradation of Lace's character.
I think it's pretty obvious—yes, my logic on this matter isn't based on any subjective preference for "Lace being a child." On the contrary, it is pure proof by contradiction. Since "Lace is an adult" completely clashes with how the plot is actually presented, then out of the two possible options, "Lace is a child" is clearly the more accurate one.
Establishing a character's narrative role is indispensable when discussing the canon lore. If a specific character interpretation directly impacts whether the overall story makes sense, I believe it absolutely warrants a discussion.
In conclusion, out of trust in Team Cherry—and assuming they didn't write a sloppy story—I believe that viewing Lace as a child is currently the best choice to minimize narrative contradictions.