LITTLE MAN: Fidel Garcia Serrano, 8, slips under his mother's wheelchair to replace a hand brake. During a period when his mother grapples with post-surgery depression and feelings of isolation, Fidel takes on added family responsibilities, watching over his brothers, doing extra chores, and helping his father but are sometimes more that than an 8-year-old can bear.   Eight-year-old Fidel snatched the toy from Tito's hands just as he was about to bash an unsuspecting Daniel. Unrepentant, Tito scampered to another corner of the porch and began tossing dirt with his toy shovel. Struck by a spadeful, Daniel tossed back a few clumps of grass. Soon, the pristine porch looked as if a twister had whipped through. Fidel shook his head and groaned. Kids, he thought disgustedly, grabbing a broom and sweeping the porch -- again. He hoped his mother would get better soon. Oh, he knew she'd never walk again. That didn't matter. He just wanted to talk to her. He wanted to tell her about the messes Tito and Daniel made. He wanted to show her how he could make a ham sandwich all by himself. He wanted her to say it was OK to be scared of the fourth grade. And most of all, he wanted her to rock him to sleep the way she used to, because he was so tired. But she didn't. She hardly did anything at all now. She just sat and watched television. His dad helped Ñ sometimes. He'd wrap his arms around him and, for a little while, Fidel could be just a boy again. But at other times, his father would sit alone in the darkness of the kitchen. He wouldnÕt move for hours. Every once in a while, Fidel would hear him sigh. Then, Fidel knew he would have to be strong. The way he was in the hospital, when he tried to make sense of all those big English words for his father. The nurses and doctors had smiled and called him "a little man." He hadn't wanted to be. He just wanted his dad to fix things. But then he had seen his father's eyes the night the ambulance came. He had seen the tears stream down his face. It was the first time Fidel had seen his father cry. And he had known the truth then: There are some things even fathers can't fix. So now, here he stood, on the porch. Trying really hard to be the little man everyone said he was. His father and mother were inside. Not speaking. Fidel rubbed his nose. He wished things would get better soon. He really was very tired. Out of the corner of his eye, he saw Daniel pick up the clumps of grass. Then he watched Tito shovel dirt back beneath a hedge. Kids aren't so bad, he thought.