Tell them that the garter snakes will eat bugs and mice.
Plus one. IMHO you should use this as an opportunity to learn and teach. I grew up in the city but in my youth my mom and dad took us camping a lot. In addition we lived on one of the numerous canyons in San Diego. I encountered plenty of snakes growing up. My dad made sure that we could identify the dangerous snakes so that we could keep a safe distance. Unfortunately there were times that we had to kill a few (once I killed a 5 foot Western Diamondback that decided to make our garage it's home) but for the most part we left them alone.
Learn to identify the dangerous snakes from the beneficial ones and teach the family how to as well.
