Not just children under 4. There is a study going around that found 12-15 year olds are ~5X more likely to be hospitalized due to vaccine induced myocarditis than hospitalized due to covid.
Some of my verbage was off but from the article:
"boys aged 12 to 15, with no underlying medical conditions, are four to six times more likely to be diagnosed with vaccine-related myocarditis than ending up in hospital with Covid"
"About 86% of the boys affected required some hospital care"
Table 2:
Age 12-17 boys Comirnaty (Pfizer): 10.6 per 100,000 doses. 1/10000.