Military dependent rank in National Cemetary burial?

This thread got me thinking. My mother had a baby who died the day he was born, lived long enough to be Baptised, I’m pretty sure. Parents are WAY Catholic. My Dad was active Marine Corps at the time, and my littlest brother was buried at the National Cemetary in the town I grew up in. I looked up his grave on this site, and it shows him as a PFC, US Army. Date of birth and death the same day. Dependents are eligible for burial in National Cemetaries, but why would they give him a rank, and for goodness sake, why an Army rank?