I wouldn't be concerned at all. In order for the teacher to have been hired by the school (if it's a public school) she has to have been trained and certified to teach elementary school aged kids. She'll have been given lots of information about the state's curriculum and as a new teacher she'll be under some form of observation / review for the year. Hopefully there's more than one kindergarten class at the school and if so, she'll get lots of support from the more senior kindergarten teachers.
Having a new teacher can be a really great experience. They often have lots of energy and tons of new ideas they've been dying to try out. She's probably really excited to finally have her own kindergarten classroom. She'll also have lots of empathy and understanding for the kids and their "preschoolerish" behavior at the beginning of the year since she's most recently worked with kids of that age.
Yes, she'll be experimenting a bit and not everything she does will be perfect. Try to be supportive through the rocky spots if they happen.
I wouldn't worry at all about the fact that your son as a new kindergarten teacher!