Deep question

I was trying to humor a child of six. Our conversation meant nothing other than to keep him occupied while his mom shopped so he wouldn't start crying or acting up.

Out of the blue he asks, "There can't be tomorrow if there is no today, can there?" Dame kid's question has been messing with my mind for two days now. I don't know if he intended it to be so deep and philosophical, but I intend to get back to him with something as equally profound.

Any suggestions would be much appreciated.