Hello Kim. Glad you found the website. Just two more postings and you'll receive your Yellow Belt!
Regarding your son, I am impressed that he is asking such questions. To wonder about the origin and destiny of the universe shows a growing intellect, and desire for understanding the way our universe works. This could lead to many great endeavors in his future. Of course we don't know how the universe ultimately began or how it will end, but we do have some ideas, some theories as to what happened or might yet happen. You could tell your son that we don't know those answers yet, but there are many people seeking those answers and he could be a part of that when he gets older. Encourage him to prepare his brain now by studying hard and doing well in school, and understanding will come to him later.
I recommend that you encourage your son to continue asking such questions, and also to seek out and read everything he can on the subject. You're right, the anxiety is not such a good thing. However, I think that by actively studying and seeking his own answers, your son can replace any anxiety he might have with excitement. Anxiety probably arises when you don't feel you have control or you don't have a firm understanding of a situation. To be active in a quest for understanding the Universe is certainly exciting and does give a sense of control as you learn more about life's mysteries and they become less mysterious. Knowledge is the key to freedom of the mind.
Good to have you with us Kim. See you around. --Robert