Not only that, but they seemed to become full grown in about as much time as it took for them to "hatch." There are a lot of inaccuracies in the film, but I still think it was worth seeing. The action scenes made up for it.
Just a little trivia, but the original Predator was a 'crab-like' creature which John McTiernan filmed two scenes with before sending it back to the studio. The actor originally cast in this role was 5'10" (1.78m) tall Jean Claude Van-Damme. Stan Winston came up with the final creature design on a flight to Japan, and cast 7'2" (2.18m) tall Kevin Peter Hall to play the Predator. It was felt that Hall was more of a threat to the bodybuilding actors in the film. Since Hall was always cast as monstors or sub-humans (he was bigfoot in Harry and the Hendersons, for example) McTiernan also cast him as the black helicopter pilot in the end of the film so that Kevin would finally show his face on-screen.
A lot of this is on the new DVD set that came out in the past few weeks.