Severe anxiety or "shyness" in kids can affect their ability to learn new things and hence, can severely affect their performance at school.
So early intervention here is definitely worthwhile.
In Australia, Fun Friends program is an option for parents to consider for their child, and it is based on Cognitive Behaviour Therapy (CBT) principles. It is a group based program. It helps the child to learn more about how to be "brave", how to understand thoughts and feelings are related, how to relax, how to learn new things through small achieveable steps, and in essence, learning how to be more emotionally intelligent and resilient. This program is not suitable for every child so explore it with the facililator prior to starting. In Australia, these programs maybe available through your local schools or kindergarten so enquire there.
You can also click on this link to find out more about the Fun Friends Program.
In my practice, I prefer to do this one on one rather than group based. This is probably because I have never been trained in "crowd control"! I try to highlight to parents that anxiety is neither good or bad. It can be very good if you can "harness" it. Overall my approach is to help parents to understand Cognitive Behavioural Therapy (CBT) and Acceptance Commitment Therapy (ACT) concepts, and then help parents to "coach" their child through co-regulation with these techniques and strategies.
This process helps both the child and the parent to become more "emotional intelligent"and resilient, because teaching is one of the best ways to learn.