This is often a question that children ask their parents. If the parent has religious beliefs then the answer is simply yes, and is usual accompanied by an explanation about having faith.
But if the parent is a non believer then it gets a little trickier. A scientific argument could be offered stating that there is no proof. But that is limited by the inability of science to measure anything that is non physical.
An alternative approach we would suggest, is to say, “That is what you are here to find out!”
Then explain to them that people thoughout all the ages have sought the answer to that question and seemingly some found an answer. These answers are found in Spiritual books around the World. However, the point is not to just accept what is written but to discover it as an absolute Truth for yourself. That is why we, your parents, are encouraging you to explore the limits of your senses and see what you can find out.