Before You Were Born, or Not

Several times now, Gavin and I have watched an episode of Samantha Brown's Europe and I see places Shannon and I have been. I tell Gavin, "Mommy and daddy have been there. We went there before you were born." And he questions, "I wasn't with you? Did I stay here with Shelby?" (the babysitter). I tell him, "No it was before you were born. God hadn't created you yet. So it was just daddy and I." He thinks for a second with his eyeballs looking up to the sky and really doesn't get how this is possible. How could we possibly existed before Gavin? Really how did we? What did we do with all of our time?