If a child has a vsd are there certain activities we should not let him do?

No. If a significant vsd is present, it is usually repaired in the first few years of life. Once repaired, there are usually no activity restrictions. A vsd that is small and does not require repair also does not require activity restrictions.
Depends. This depends on the size of the vsd and if there are any other problems. In general, the child should be able to engage in age-appropriate activities. Scuba diving (not age appropriate) and other risky activities may pose a problem, but again, shouldn't be an issue. Discuss your child's specific limitations with their cardiologist.
As tolerated. Once surgical correction of the vsd, activity is as tolerated once the sternum has healed.