Sociologists have defined her. Psychologists have analyzed her. Pollsters have surveyed her. But here's what those who know her best -- children -- have to say. Liz Ann, age 8. "Who is a mother? She knows what is important. This is why God asked her to be a mother." Louise, age 7. "A mother is the only one if she sings your favorite song it stops thundering." Jimmy, age 8. "A mommy is a wife. A mommy looks after children and she yells." Gary, age 6. "A mother doesn't do anything except she wants to. Nobody makes her take baths and naps or takes her frog away." Harry, age 8. "If I forget to tell my mom I need my shepherd costume tomorrow morning, she finds one in the night. That is a mother." Laura, age 6. "Mothers are wonderful! She spends all her time on you. A mother is …