Two Families

When Dr. White and Dr. Green met each other 5 years ago, each family had only one child. Now they each have two children under 10 years old. These are the facts about their children:
1) James is the oldest among the four;
2) Russell is 4 years older than his brother;
3) Stephen's age is half of one of Dr. White's children's age;
4) Kevin is 2 years older than Dr. Green's younger child.
If each child is a different age, how old is Stephen?