This was announced in the press conference held by Maryland Governor Larry Hogan on March 19, 2020:
“Among today’s new cases is a 5 year old girl in Howard County who has tested positive for COVID-19. The first case of a child contracting the virus here in Maryland”. See that part of the announcement here:
You can watch the full press conference here: https://www.facebook.com/GovLarryHogan/videos/257951838541640/
Maryland Department of Health reports 16 confirmed cases of Coronavirus in Howard County and 107 cases in Maryland on March 19th. You can read that article here: https://scotteblog.com/2020/03/19/maryland-department-of-health-reports-16-confirmed-cases-of-coronavirus-in-howard-county-and-107-cases-in-maryland-on-march-19th/
If more details are released from Howard County officials I will update the blog.