WE BEGIN IN a place called Fort Dix, N.J., where, on a day remembered as cold and drizzly, there reported to the grenade range a certain Company D of the 4th Training Regiment ("Second to None"), led by none other than Pvt. Richard Cohen. It was thus that he became the first in his company to toss a grenade, a turn of events that did not faze him in the least, since he not only had a pretty fair throwing arm but had seen lots of war movies as well. He threw. He ducked.He realized immediately that the movies had lied.

There was no polite puff of smoke followed by rolling noise like thunder over the mountain. There was, instead, a sharp explosion and a whump that took the air and flung it back at him - a terrifying, unexpected concussion. It was not at all like the movies, and while you might say that nothing really is, it is always a surprise to find that to be the case.

This seems to be the case now with children. Lots of people assume, it seems, that the kids they see in the movies are The Real McCoy. In fact, true kids have virtually been banished from the silver screen only to be replaced by wise-cracking pygmies - child lookalikes armed with the one-liner repertoire of a Henny Youngman. As far as you can tell from a recent spate of movies, kids differ from adults only in that they are a bit wiser and go to bed, sometimes, a bit earlier. This, as my old grenade sergeant would say, is not the way it is in real life.

It's hard to tell if this is a case of the movies imitating life or the other way around, but some of it probably has to do with the whole liberation movement - women, men, homosexuals, animals and children, in no particular order. With children, this means that they are no longer to be treated as children, but as little adults, companions, pals. In the movies, where restraint and subtlety are almost unknown, the kids emerge as if they were Groucho Marx with a glandular problem - small, maybe, but very witty and a bit world-weary.

In real life, this takes the form of adults treating kids as if they were, in fact, adults. They use language before kids that they would not use down on the docks, and while in the movies the kids soak it up, in real life they bounce it right back at you - often in a place like church. People turn on in front of their kids and talk sex in front of them, and if some reports are to be believed, they "do" coke in front of them. They tease and use sarcasm and employ double entendres and then wonder why the kid cries. This is not the way it is in the movies.

In the movies, the kids are like Tatum O'Neal in "Paper Moon." Here was a kid who not only had all the answers, but smoked as well. While it was recognized that she was a child, it was also understood that she was in some ways more mature than adults - wiser because she was purer. This is a sort of updated version of Rousseau's Noble Savage, the thinking here being that wisdom is lost with age.

You saw something like this in the show "Alice Doesn't Live Here Anymore," in which the kid was about 12 but infinitely wise. His mother would turn to him for solace and while once in awhile he would do something childish, it was a mere nothing compared to her affair with a man who turned out to be a woman-beater. The kid would not have done anything quite so silly.

There are lots of examples of this sort of thing and there's probably an element of truth to these portrayals. They are, at the very least, a bit more honest in their own way than the pictures-of-old where curly and empty-headed moppetts either tap danced across the screen or forever went chasing after dogs named Lassie. So what we are seeing, maybe, is a reaction to all that - Hollywood making up in spades for the sins of the past. Nowadays, they would give Shirley Temple a song-and-dance routine about the Pill and send her out as a groupie for the Bad News Bears.

Anyway, the upshot of this movement is that we've made "people" out of children, liberated them both in life and on the screen, created strange little creatures that are neither adult nor child. What they resemble, in fact, are the screen women of yesteryear. Children are now the one who talk tough, but really aren't; who pretend to be sophisticated, but of course are not; who would, when things get tough, turn soft and childish and show their true colors.

The best you can say for all this is that women are not as they are shown to be in the movies. You learn that sooner or later - usually the hard way. The same is true of kids. You learn that the day when some kid asks you a question and you give him some wise guy answer just like in the movies, and instead of the kid smiling, tears well up in his eyes. You wonder what you did wrong.

You realize very quickly that the movies have lied.