Hello,everyone.I'm Lucy,I'm a girl,I'm six years old,I'm a student.I have a happy family.There are three people in my family,my father,my mother and me.My father is a worker ,he is very strong;my mother is a teacher ,she is very clever;I'm their sweet heart.I like drawing and playing badminton.I believe "No pains ,no gains".I have a dream---I　wish the world is peaceable　

原文
Hello,everyone.I'm Lucy,I'm a girl,I'm six years old,I'm a student.I have a happy family.There are three people in my family,my father,my mother and me.My father is a worker ,he is very strong;my mother is a teacher ,she is very clever;I'm their sweet heart.I like drawing and playing badminton.I believe "No pains ,no gains".I have a dream---I　wish the world is peaceable　

呵呵，首先，一个6岁的小朋友能这样写已经不错了，不用强求她用太深的词汇，但是如果文章出现太多的I'm就会显得冗繁，不如这样写
Hello, everyone. I'm Lucy, and I'm six years old now.(这个student不知道她上学没有哦，因为把学生加在这里显得与前后文联系不紧密。) I have a happy family. There are 3 people in my family, my father, mother and I(这里不需要用宾格). My father is a worker, he is very strong; and my mother is a teacher, she is very clever. And I'm the sweet heart in their eyes.(那样说有点别扭). Drawing pictures and playing badminton are my hobbies.(前后对应,句式也多样一些。) I believe "No pains, no gains." I have a dream, that is(不知道她是要交给老师看，还是读给大家听，用that is更加地道一点。)I wish the world will be peaceful.（额，peaceable好像不太对，而且是“希望”后面用将来时更好一点。）