Oh, and my picks are:
A seven-year-old Angelina Joelie in Looking to Get Out.
Miguel Sandoval in Repo Man. He’s Archie, the guy with the Mohawk.
Brad Pitt in a blink-and-miss roll in Less Than Zero. You see him for a second in the fight scene at the end of the movie.
In The Charge of the Light Brigade(1968), you can see a small tow-headed young girl featured prominently in a couple of early scenes at the outdoor party. That is the director’s daughter, and those scenes have no bearing on the rest of the movie, just a chance for proud dad to say, “Look at my beautiful little girl:” Natasha Richardson.
Similarly, I’m 80% sure that the crying toddler in the airplane with Robert Morse at the beginning of The Loved One (1965) is also Richardson–but I haven’t been able to corroborate it.
Lance was mistakenly added as being killed by an alien. Actually, he survived the Alien in Aliens. In Alien3, the beginning of the film said he was one of the survivors on the escape pod/ship (along with newt, Micheal Biehn, and Sigourney Weaver,) but when it crashed on the prison planet, only Weaver survived.
On that note, Chris Rock was the valet at the Playboy mansion in Beverly Hills Cop II.
Youtube time
In the one odd reversal of this that I can think of, I spotted Carl (Alfalfa) Switzer in his teen role in It’s A Wonderful Life. He appeared in other films, but I’ve never recognized him.
He had a significant role in The Godfather II as the young Clemenza.
Pre-glee Jane Lynch as Old Christine’ son’s principal, Allan and Charlie Harper’s therapist and Spencer Reid’s psychotic mother.
Pre-That 70’s Show Debra Jo Rupp as Seinfeld’s agent and Friends’s Phoebe’s sister-in-law.
I won’t hijack this thread, I won’t hijack this thread, I wo–Oh, yes I will . . .
Welllllll, thanks to the alien, Ripley had to pull the plug on ol’ Lance on the prison planet. I’d say we’d at least have to give it the assist. If a robber shoots a guy, and seven days later, they pull the plug on life support, it’s still the robber who kills him, not the doctors.
And so it’s not a total hijack, William H. Macy in 1980’s Foolin’ Around.
Matt Damon played the cheater who tried to pin it on Brendan Fraser in “School Ties”.
But if a guy escapes from a robber, and is later in a car crash, that’s not the robber’s fault.
It never came out on VHS or DVD (I have a copy I recorded off HBO in the mid 1980s) but Jay Leno plays one of Alan Freed’s sidekicks in 1978’s “American Hot Wax”. Not that Leno was that young, maybe 28, but it is disconcerting to see that chin as an actor when you are used to him as a talk show host.
There is some debate over whether Christine Baranski (“Cybill”, “Mamma Mia”) appeared as child actress Chris Charney in 1960s shows like “Combat” and “Brady Bunch”. She denies it but there is no biographical data in imdb on Charney and her career seems to end about when Baranski’s begins. I’ve seen the “Combat” epsidoe where she plays one of the girls in an orphanage and it looks like her (the caved in face cheeks).
Not any more. I won’t post a link to her profile, but Ms. Charney is on facebook, and is about 4-5 years younger than Baranski. Having said that, there is a resemblance.
Sadly, I’m going to have to let this great trivia go. 
It was one of my favorites too.
He obviously survived being torn in half by the alien, and the next movie confirms it.
Maybe we should start an online petition or something to get him killed in the next franchise.
Leslie Nielson’s IMDB lists 239 credits, but I think we can all agree it was Airplane (1980) that made him a household name.
Prior to that he did lots of TV and was the Captain in the Poseidon Adventure. If you catch the PA on TV you will see that he plays the Captain in the same deadpan manner that he played Dr. Rumack. Turns the first part of that movie into… something strange as you wait for the punch line.
For that matter, Lisa Kudrow, who played Phoebe, also had a recurring role in Mad About You as the absent-minded waitress, Ursulla.
And, to further the Debra Jo Rupp connection, her husband (and Phoebe’s brother) was Geovonni Ribisi (who was on My Two Dads as a kid, which also featured Paul Reiser, who was the male lead in the aforementioned Mad About You).
Remember Paul Reiser as the slimy corporate agent in Aliens?
I would have thought you were old enough to remember him as Commander Adams in Forbidden Planet. 
In a similar vein, Bill Maher as one of the cabbies in D.C. Cab.
Warren Beatty and Tuesday Weld on “The Many Loves Of Dobie Gillis.”
AND
Laurel & Hardy’s “Way Out West”:
In front of the saloon, L&H do their hilarious dance to The Avalon Boys singing “At The Ball, That’s All.” The guy in closeup doing the yodeling is Chill Wills, who parleyed the appearance in that movie into a long film career.
.
If Excalibur get a shout out, how about The Bounty (1984)? Okay, Sir Laurence doesn’t count, but then you have Mel Gibson, Anthony Hopkins, Daniel Day-Lewis, Bernard Hill, and Liam Neeson.