I really like how you’ve set this up, using Emma’s POV to introduce the characters and their situation, and how her perspective differs from her sister’s. I also like how everything makes sense: the family experiences a tragedy, the father wants to connect with his kids on a camping trip, Emma chases a rabbit (and, I’m assuming, disappears).
Both Emma and Kayla are believable and their behaviors are consistent with what you’d expect from kids their age. I find that refreshing as a parent because filmmakers and writers alike led me to believe my kids would be far more intelligent, insightful, thoughtful, and responsible than any kid in real life actually is, so it’s nice to see kid protagonist whose behavior resembles that of actual children.
I’m torn about the pacing, though. I’ll admit, it has been a good long while since I’ve read an entire novel, so I’m not sure if the pacing is fine and I’m just inclined to tighten things because I edit short fiction every day, or if these details I noticed could actually stand to be held back and dropped into later chapters. (Hopefully, Cody and Dede can jump in; they read more long-form fiction than I do.)
I would recommend dropping a compelling hook at the end of Kayla’s chapter to lay the stakes on the table and pull the reader into the book—something along the lines of, “That’s when we realized Emma was gone.”
+ Characters are believable. + Dialogue is authentic and realistic. + Premise is compelling. + Setup is logical.
+ Pacing may need to be picked up. + The hook might need to be set a bit earlier. (Maybe. Remember, my perspective is skewed by my experience.)