It's not necessarily wrong to let them be excited about Christmas; I still remember our own children's excitement as they gathered around the Christmas tree and impatiently waited for their turn to open another present. To them, breakfast that day felt like the longest meal of the year!
But once the excitement dies down, take time to teach your children about the greatest Christmas gift of all: the Lord Jesus Christ. Each of them will probably have a favorite gift once all the presents are opened, and they'll probably be happy to talk about it if you ask them. However, some day (you might point out) that gift might break or be lost, or they'll grow tired of it. It's probably happened with something they got last Christmas.
But remind them that God's Christmas gift to us never grows old or gets broken -- because His gift is eternal. Jesus Christ was God's Son, sent from heaven to save us from our sins. When we put our faith and trust in Him, He promises us the gift of eternal life. This, the Bible says, is "an inheritance that can never perish, spoil or fade -- kept in heaven for you" (1 Peter 1:4).
Your day might unfold differently -- but whatever happens, ask God to help you remind your children why we celebrate Christmas. Then ask God to help you make Christ the center of your life -- and your family's life -- every day of the year. May Jesus' command become your goal: "Seek first his kingdom and his righteousness" (Matthew 6:33).