Parents are an important part of the school system. Parents and extended family (ie. brothers, sisters, grandparents, aunts and uncles) are the very first teachers of each child. You have known your child longer than anyone else and you know how your child responds in many situations. Your participation in school is highly valued.
Anxiety Canada has tips for parents here (as well as a wealth of information if they or their child has anxiety)
This website has a cute poster that pretty much summarizes the tips from the above site
This is a longer article and video about supporting your child going back to school