Why can't we see God or Jesus?

I was talking with my four year old today. He started telling me that Jesus was greater than anyone and that people are not perfect. He heard a song on the radio that talked about the fact that there are no perfect people. He started mentioning the fact that nobody could see God or Jesus. I asked him why that was (mainly because he has asked me that question himself in the past and I wanted to find out what he had understood and retained---nosey mom that I am).

He didn't remember why to my chagrin, but we just talked about that we can't see them with our human eyes, because they are weak and not perfect. But when we die and go to heaven we will get new bodies with eyes that can see God and Jesus, glorious bodies that will never get hurt or sick or sad.

That is the easiest was I know of explaining it to children. It is the same with the Holy Spirit. I use the example of the wind, how we can't see it, but we can see its effects when it blows our hair, a leaf, trees,etc. If little ones, or even big ones of us, have trouble believing in a God and Lord that are not visible, try this example to explain it. At some point it must come down to faith. It is a hard concept for adults to grasp (and to find faith in), let alone children with limited knowledge. Anyway, I hope that example helps you when your children ask about the spiritual vs. physical.

John 20:29 "Because you have seen you have believed. Blessed are those who have not seen and yet believe."