Up until 2019 at least, automobile deaths were the #1 cause of "child fatalities". During the pandemic, when schools were closed, businesses were shuttered, and people were advised to stay home, there were fewer people driving including 16-19 year olds -- just happens to be within the group having the most car crashes: 16-26.
Firearms were second for the longest time, with drowning a distant 3rd.
For any stat you can pick a given year or other period of time in order to make things look better or worse than other times.
Still, the inclusion of 18-19 year olds and a 38% suicide rate among their "child" grouping shows how dishonest these people are, and how willingly the media spreads this lies without an ounce of fact-checking.