My 3-year-old is having an existential crisis

Last night, while reading an earlier installment in the Berenstain Bears series:

Sydney: "Where is Sister Bear?"
Mommy: "This story takes place before Sister Bear was born, so she's not in this story."
S: "But why is she not born?"
M: "Because...uh...because it hasn't happened yet."
S: "Is she in Mama Bear's tummy?"
M: "I don't think so, not yet."
S: "But where is she then?"
M: "She's not alive yet."
S: "What's 'alive' mean?"
M: "Alive means you're born."
(Pause)
S: "Am I alive?"
M: "Yes."
S: "And Baby Evan?"
M: "Yes."
S: "But where was I before I was alive?"
M:
S: "But where was I, Mommy?"
M: "I'm not sure, sweetheart. You just weren't here yet."
(Pause)
S: "Mommy?"
M: "Yes, baby."
S: "I don't like that."