4 BIRTHDAYS MENTIONED IN THE BIBLE, theJW say only 2.
Birthday of Pharaoh, criminal was beheaded (Gen;40:20)
Birthday of Herod, J the Baptist was beheaded reluctantly (Matt; 14:6)
Birthday of Job's sons "held a banquet at the house of each one on his own day". (Job:1:4)
Birthday of Jesus. The birth of Christ, celebrated by the angles in song and glory. (luke 2:10-14)
The rules of the Watchtoer
To celebrate a Wedding and buy gifts? OK
To celebrate the birth of a child and buy gifts? OK
To celebrate the anniversary of a wedding and buy gifts? OK
To celebrate the anniversary of a birth? NO - PAGAN
I got this above info from www.uq.net.au
So tell your son if the angles in the Heaven can celebrate Jesus the Kings birthday and can get gifts, then yes it is right that you celebrate his Birthday as well.
AND HAVE A BIG SPLASH
Then tell him "just you wait for Christmas"