First the ones you probably have heard of:
Gary Matthews and Gary Matthews, Jr. The Sarge put up some great numbers with the Cubs and helped lead the team to the Eastern Division title in 1984. Junior was with the team in 2000 and part of 2001 before he was released in August.
Randy Hundley and Todd Hundley. Randy was the catcher of the memorable teams of the late '60's and early 70's. He was hit by the injury bug in 1970 and never played a full season after that. Son Todd came to the Cubs in 2001 with great expectations. He grew up in suburban Palatine and this was his homecoming. Maybe the pressure of playing for the hometown Cubs and being Randy's son was too much, or maybe he just sucked. But he was terrible with the Cubs hitting .187 and .211 while striking out a ton. He was dumped on the Dodgers after the 2002 season.
Three lesser know Cubs father and son combinations include:
Marty Keough and Matt Keough. Marty played the last 33 games of his career in Chicago, while Matt spent part of his last major league season with the Cubs.