I wish I could go to the school where my close friends go, but I obviously can't. The good thing is, they're really good about inviting me to all the football games and all that stuff. So I end up having an adopted team spirit for a school I don't go to.

He's also notable for having voiced Riku in the Kingdom Hearts video game franchise and for portraying Seiji Amasawa in the English dub version of Studio Ghibli's Whisper of the Heart. In 2005 David starred in and co-produced a low-budget adaptation of The Picture of Dorian Gray. Then in November 2008 he appeared in an episode of the CBS show Without a Trace as a suspect named Jeff Ellis who was thought to be responsible for the disappearance of a local nurse.

Beginning a prolific career as a child actor and model at the age of two Gallagher is a five-time Young Artist Award nominee and Teen Choice Award winner best known for his role as Simon Camden on the long-running television series 7th Heaven as well as for his feature film roles; as Mikey Ubriacco in Look Who's Talking Now as Kevin Harper in Angels in the Endzone and as Richie Rich in Richie Rich's Christmas Wish.