Are these people biracial or not...?

I know this guy, who has three kids, he is black, but still has white grandparents on his mother and fathers side,one of them looks like him,but the other two...well...they both have light hair...thats straight...the girl has blue eyes, she doesn't even have one thing that makes her half cast, maybe quarter cast, but she just looks caucasian, and so does the boy...well...is it possible for a black person to have two kids who ARE white? because i think these kids arent biologically his...thank you