SADS is nothing new and I can find no studies that link it to covid vaccines.
Sudden Adult Death Syndrome is not a COVID phenomenon
www.healthing.ca
Reports of sudden arrhythmia death syndrome (SADS) date back to the early 1990s. SADS is the result of genetic mutations that disrupt the electrical system that regulates the pumping action of the heart. This can lead to abnormal heart rhythm (arrhythmia) and sudden cardiac arrest. Some people...
healthfeedback.org
That said, there is a slightly increased risk of myocarditis, especially in young people, and an extremely low to zero risk of serious illness or death from covid in healthy, young children. Given that these vaccines do NOT prevent spread of covid, so the "it's to protect Grandma" argument is gone, I can't think of any good reason why someone would inject a healthy child with these current vaccines.