A high-ranking official said the hospital currently has hundreds of open positions and attributes much of the staffing shortage to the COVID-19 vaccine mandate.The largest children’s hospital in Wisconsin has been struggling to care for patients in injured in the Waukesha Christmas parade attack on Nov. 21 in large part because of staffing shortages stemming from its COVID-19 vaccine mandate, multiple sources say.Eighteen children were brought to the Children’s Wisconsin Milwaukee Hospital with injuries suffered when a driver plowed into parade-goers that Sunday afternoon. Several remain in critical or serious condition, and an eight-year-old boy died of his injuries Tuesday....