The issue of severity is one of the markers that would elevate a variant to a variant of concern. The determination of increase in severity is work that has been under way for the three variants of concerns most reported to date. Preliminary results from the U.K. suggest that there may be an increase of severity among older individuals affected by the variant first identified in the U.K., not children. But these are fairly complex epidemiological studies that have to take multiple factors into account, including the strain on health systems, so the precision of the estimates will be lagging as the science evolves.
On February 19th, 2021. See this statement in context.