The Bible doesn't say anything about life on other planets; its focus is on this planet and its need for God. There well may be life on other planets - but the Bible simply doesn't say one way or the other.
What the Bible does say about the universe, however, is very important - and I hope you'll teach it to your son. It's found in the very first verse of the Bible, which tells us that everything in the universe was made by God: "In the beginning God created the heavens and the earth" (Genesis 1:1). The galaxies and the stars and the planets didn't happen by accident; they came into existence because God made them.
And the same is true of all life - including us. We are here because God put us here - and He put us here so we could know Him and serve Him. God loves us - and the proof is Jesus Christ, who came down from Heaven to save us. The Bible says,
"This is love: not that we loved God, but that he loved us and sent his Son as an atoning sacrifice for our sins" (1 John 4:10).
Be thankful for your son's curiosity - and ask God to help you use it to point him to Jesus. (Many parents find a children's Bible story book helpful for this; your local Christian bookstore can suggest several.) Make sure most of all of your own commitment to Christ; the greatest gift you can give your son is your example of a strong and vibrant faith.