Wonder what happens if I buy one of these…

That sounds like tinnitus

Alongside what others have recommended, I’ve found that running through scientific case examples and trying to get them to come to the conclusion themselves (for example pointing out that a river dips to a certain area or that vegetation in an area is missing) helps to teach critical thinking without a pro or anti-religious bent. It’s also a tad bit of a buzzword today, as it encompasses many skills, but in my opinion (which isn’t the only one) one of the most important base skills is a firm understanding of hypothesis tests.