I assume your husband's employer has obtained professional assistance with the legal immigration issues - work and residence permits for himself and the family.
I would also recommend professional relocation assistance to help you orientate and settle. The American International School of Johannesburg is located to the north of the city towards Pretoria. as is Dainfern (golf estate) and other fully secure gated communities. I would strongly recommend that you ask your relocation service provider (paid for by the company) to search out suitable homes in that area, and to arrange for you to speak to the AIS. The fees at the AIS are expensive and it is usual for the employer to fund them.
Joburg is a very friendly place and I am sure that if your son attends there and you live in one of the gated communities you will make lots of friends, both American and local and have a great stay here in our city.
Crime is an issue to be respected rather than feared, and if you take suitable precautions and remain aware at the points of danger you will have a safe and fear-free time. Again your husband should ask for a securit briefing from a relocation company - avoid the security companies as it is their business to scare the life out of you so that you will make extensive (and expensive!) use of their services.