Allen got his first notable role as the headstrong pre-teen son of Deidre Hall (and younger brother of Shannen Doherty) on the heartwarming family drama "Our House" (NBC, 1986-1988). He also played the cooler of the two school friends competing for Staci Keanan on "My Two Dads" (NBC, 1987-1990). His most fulfilling role to date, however, was Matthew, the eldest (and most strong-willed) of the orphans adopted by "Dr. Quinn, Medicine Woman" (CBS, 1993-98). The role gave Allen a showcase for his maturing talents. In 1996, his character was even elected sheriff.
Allen was a tiny tot when he made his first TV-movie, a bit in the drama "Not My Kid" (CBS, 1985). Slowly-growing roles followed in "The Bad Seed" and "A Death in California (both ABC, 1985) and "Code of Vengeance" (NBC, 1985). In 1986, Allen voiced the lead characters in the animated "Happy New Year, Charlie Brown!" (CBS) and "Pound Puppies" (ABC). From then on, his roles were starring or co-starring: a "rental" in "Help Wanted: Kids" (ABC, 1986), a resident of "Camp Cucamonga" (NBC, 1990), a teen seduced into evil in "Murder in New Hampshire: The Pamela Smart Story" (CBS, 1991) and the son of potential murder victim Barry Bostwick in "Praying Mantis" (USA, 1993; Dr. Quinn herself, Jane Seymour, played the villainess).
Allen's only theatrical film thus far did not appeal to either critics or audiences: he played the heroic teen who tries to protect his family from a space alien in "TerrorVision" (1986). The politically active actor is involved in such groups as MADD, The American Diabetes Association, The Autistic Children's Foundation and Angel's Flight, a teen halfway house. He also appeared in a 1988 anti-drug special, "Straight Up" (PBS).