I would try to have them around other black kids as much as possible through programs and social activities. My parents had exposed us to a lot of different things including being around white people, some situations where we were the only ones or one of few. But the home base, family, friends, and other programs were Black people.
Keep an eye on their school, teachers, and administration. They are always trying Black kids and letting white kids get away with murder. Seriously. Honestly having a child in a predominately white school you are always in question. Then it is a struggle, because you can't be there all the time. Do you ruin their innocence? Tell them what to look for, what could or did happen? How soon do you tell them about the real world? This goes for a white area too not just school.
Keep communication between you and your sons open as possible so they will come to you if things happen. So if you are trying to shield them for the time being, they tell you, you catch it and handle it.
Teach them to be proud of being Black and that it doesn't mean acting a certain way. They have to have a strong sense of self or a good foundation period. Even going between different black areas for me personally, there was some culture shock initially in school (from a private black school to a public one). They called me proper girl and made some other comment about me but to me I knew what I was, who I was so that didn't make me try to "fit in". I was around all types of Black people, All incomes, all attitudes and one thing didn't necessarily determine another, so I never bought into stereotypes.