Here is my letter. I student taught for an entire year which is why mine is a little different. Try to just keep it short and sweet.
I also printed mine off on some cute paper and a fun font...you don't have to do that obviously, I just enjoy that sort of thing! haha

Good luck student teaching, it is the most eye opening experience of your teaching career!
Dear Parents,
Hi, my name is *******, and I am an Early Childhood Education major at Illinois State University. I am going to be the student teacher in this class for the entire school year. The first semester I will be here 3 full days a week and the second semester I will be here full time.
I just got married over the summer and am living with my husband, Jason in our house in *********. I was born in **** but have lived most of my life here in ********. In my free time I enjoy scrap booking, running, shopping, and spending time with my family.
I love working with children and am really excited about this year. I look forward to having your child in our class and getting to know them better.
If you ever have any questions, or if I can be of any assistance, please feel free to contact me.
Sincerely,