They have lost their places in the starting XI because of new signings and less Villa injuries.
"They must understand they have to build up their game," Houllier told the Birmingham Mail. "Sometimes they must work and develop without pressure of a game.
"There must be less waste. They must be confident about beating players, crossing and passing.
"Lionel Messi didn't play every game straight away, it takes time. Young players have to learn, they can't be always start every week.
"Their impatience is reassuring but it must not hold them back. If you overplay them you burn them out."