Waldrop, a lefty hitter, batted .273 with one homer and five RBIs in 12 games. He was the organization's Minor League Hitter of the Year in 2014 and is ranked the Reds' No. 14 prospect by MLB.com.
Sampson posted a 2.25 ERA with six hits, one walk and four strikeouts over eight innings in four games.
Magill, who came over in the December trade that sent Chris Heisey to the Dodgers, had two scoreless innings in two appearances.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.