Mommy, where did you put Julia's bones?

Mattie, out of nowhere mind you, asked me this afternoon, "Mommy, where did you put Julia's bones?"  I was certainly taken off guard by this question!  I responded, "Are you asking because people sometimes bury people when they die and you want to know what happened to Julia's bones?"  She said, "Yes."  I was not feeling quite ready to answer this question and I certainly didn't really want to answer without talking to Bob about it.  So I told her that I wanted to talk more about it but I'd like to wait and talk about it all together when Daddy got home.  She seemed okay with that.  So after dinner, Mattie was occupied with the iPad and so I summoned Bob to the back bedroom to tell him what Mattie asked today.  He was equally taken off guard.  We decided we would wait until Mattie brought it up again since it was close to bedtime for Mattie.  We're still not totally certain how to answer her question... we cremated Julia and we're not sure how to explain cremation to Mattie.  But we're thinking about it and have talked through an acceptable answer for now.  Any advice is welcomed!  I'll keep you posted as to how we answered it when we finally do.