I'll give you three guesses about who you think Marvin Harrison, Jr.'s dad is.
Michigan just offered him, which I figured for a while would be coming. He goes to Philadelphia (PA) St. Joseph's, which is the same school that Jon Runyan, Jr. attended. Harrison had 50 catches for 725 yards and 8 touchdowns as a sophomore. 247 ranks him as a 4-star, the #3 receiver, and #16 in the 2021 class, although it's still early.
Jim Harbaugh was with the Colts through 1997, and Harrison's dad was drafted in 1996, so they have a little bit of history. He caught 14 touchdowns over those two seasons, though I'm not sure exactly how many came from Harbaugh.
Here's a link to his Hudl (LINK).