The incidence of COVID-19 remains low during childhood. Numbers are quoted to be between 2% and 12% (depending on testing) with a general milder course but variable symptoms that may mask the viral infection and delay in making the diagnosis.
Despite common sense that preexisting cardiac diseases should impose children with congenital heart disease to a higher risk this has only rarely been demonstrated so far. 
The following strategies should minimize risk of cardiac surgery during COVID-19 pandemic:
Pediatric heart catheterization and intervention in COVID-19 patients has been done as an exemption in some cases. Elective cases have been generally postponed in the beginning of the pandemic. Meanwhile, as the numbers of affected children remain low, it seems reasonable to activate the programs while continuing PPE and following institutional flow algorithms for COVID-19 patients, including switch to negative pressure environment in the cath lab if possible (see also paper on AEPC-website, WG Intervention). A comprehensive guidance paper addresses most aspects of decision making and resource allocation.  The subgroup of adults with congenital heart disease are likely to have the highest risk within patients with congenital heart defects  as at least in complex cases they cover the aspects of premature aging of their hearts together with limited cardiac reserve and lacking the advantage of children that are in general less susceptible to symptomatic SARS-CoV-2 infections.
Heart transplantation / Immunosuppression: While immunosuppression in general enhances the risk for viral infections and increased severity as has been described for younger children with influenza, this does not seem to be the case in SARS-CoV-2 infections. Instead immunosuppressive medications in children may even be protective against excessive immune response. Data from solid organ transplantation do not show that immunosuppression during COVID-19 pandemic leads to less favorable outcome. Immunocompromised children, for example treated for cancer only rarely needed modifications of their treatment. Accepting that not all patients are tested for COVID-19 at least symptomatic worsening has not been observed.  Nevertheless transmission precautions are of paramount importance and should be strictly followed until further knowledge of SARS-CoV-2 impact on the immune system is available.