Another Son of God?

I am always intrigued by what the Koraan and the Bible say.- their similarities and their differences.
All this while I always thought that there was only "One son of God" in the name of Jesus Christ as claimed by the Christians, but later I discovered something else......There was another one

I was reading the Koraan (Translation by Muhammad Assad) Chapter 5 Al-Ma'idah Verse 18 where I came across the following:

"Both the Jews and the Christians say 'We are God's children' "

Then I picked up the Bible (New King James Version) to find out whether it says anything about this "God's second son".. I found it in two places:

Exodus iv 22.23 in which God says "Israel is my son. My first born"

Jeremiah xxxi 9 God says "I am the father of Israel"

For my Muslim friends who are not familiar with the names of the Biblical prophets Israel refer to Nabi Yaakub. It is from this "Israel" we get the name "Bani Israel" (The tribe of Israel) so often mentioned the Koraan