I found out at age 7 or 8 myself which I always thought was pretty late. DS (9) still talks about Santa like he genuinely believes in him.
Is this normal? DS is a pretty switched on kid so sometimes I wonder if he actually knows Santa isn't real but plays along to it because he maybe thinks he needs to in order to get presents?
At what age did your DCs find out the truth and how?
Is there a gentle way to break the news so the child doesn't feel betrayed if it goes on for too long?