I am often asked by attendees which programming language is the best to teach. The answer is simple and complex all at the same time. Of course, you would expect a programmer to tell you that...I hope! The reality is that for beginners, the language is not important. You are teaching logic. I may even suggest that some formulas in Excel would be a great place to start to understand logic. Simple "if, else" statements are mind blowing to beginners. This is a great opportunity to connect with hypothesis development in the sciences.
The answer is different depending on what the students already know when they get to you. Additionally, this is dependent on what you already know at the outset of teaching coding and your capacity to learn along the way. Let's break that down a bit...
1. What do the student know about programming and coding ahead of time?
As coding has become more popular in the last 5 years, most students have dabbled already. Many beginners work in Java or Python with Java being the more popular. They are pretty simple to understand and write. The fact is for beginners, it doesn't matter what language is chosen. Most of the online programs (Scratch, Code.org, etc.) all utilize Java for the most part. The only advice I would give is stay consistent with beginners.
For more advanced students, language becomes more important. The key is understanding one language very well before expanding into the syntax of another language. Once students understand the logic and the complexity of one language, the others are easier to master.
2. Your capacity to learn
You are busy! That is often an understatement to educators. Do you have the time to invest in learning the language, too? My advice is don't worry about the languages and try to learn more than one at a time if your formal training did not include computer programming. In this case, keep it simple! Teach one language until you have mastered it. Then, explore the others. You don't have to be perfect your first time or two teaching coding lessons. Go easy on yourself!
I hope this helps...from my own rambling experience presenting coding workshops and teaching it to my own students. Please post questions, comments, other helpful tips, etc.