Nineteen-year-old Cosgrove, who made his Warriors debut last month at Sale Sharks in the LV= Cup, was also promoted to the starting line-up in the front-row.
But the pair couldn't prevent a strong England line-up from running out 48-15 winners at Netherdale on Friday night.
Meanwhile Wales beat Ireland 16-0 and France triumphed 34-0 over Italy.
The young Warriors will be in action again when Scotland battle Italy on Friday 21 February at Stadio Omero Tognon.
England Under 20s face Ireland at Franklin's Gardens on Saturday 22 February with France taking on Wales.