A lot of work to be done in this area with hopefully more studies to come. Moderna has a higher incidence. Canada (and others) has been smart about spacing out 1st and 2nd dose, which likely helps in mitigating risk of myocarditis. There is risk of myocarditis with natural infection but incidences have been rather low and mild , just like every year with viral infections. Something about MRNA that makes this a bit different - it'swhy studies are needed and parents need to carefully assess risk/benefit.
IF you want to vaccinate your U18 boy child, highly recommend spacing out the doses - forget to come back for the second appt.... Likely no need for boosters, especially for college aged kids. Ramping antibodies for the sake of ramping up is rather foolish. it's as if some people have forgotten about the other, more important aspects of our immune system.