You wont find Census records for South Africa anywhere - they routinely destroy the forms once the data is aggregated, you probably need to look for Directories - like Braby's to see if the family appears. Civil birth records can only be obtained from the Local authorities or at the Archives - they have not been filmed by familysearch. The best bet for birth records are the church records, if the family is Anglican than you can find most Diocese records online at familysearch. If Methodist there are some but the bulk are held at the Cory Library in Grahamstown, the DRC and Reformed church records are on-line at familysearch. For most other denominations you need to approach the relevant churches