I haven't had a child like this, but I was one. As in, thought process at a year old: Oh look, the top of a sheer cliff terminating in deep water--that looks like a fun place to play tag with my terrified parents. I was also an incessant climber, lacked fear of strangers (at least as a toddler), and enjoyed balancing on the curb next to traffic. I'm pretty sure I'm alive today because my parents put a toddler-leash on me (after the cliff incident).

So yes, take it very seriously, yes, be very grateful nothing bad happened, yes, recognize the potential bad outcomes that could easily have occurred, but no, don't beat yourselves up about it (you've never parented this child before, so you're still figuring it out). Learn from the experience, and move forward.

...pronounced like the long vowel and first letter of the alphabet...