SPOILER WARNING: He's using the dull edge for the sawing; using the dull edge AND pulling his strikes for the chops. The inside curve is the sharp edge, not the outside.

He does the same with the katana, except for a couple draw cuts near the end, where he's clearly missing both the child's and his own neck by a good inch or so.

Yeah, someone pointed out that it's not the sharp edge in the comments on the Youtube video itself, although I'm really unfamiliar with that kind of blade so I wasn't sure.

It did look like he was stopping short of touching the kids' necks.

The kids are just run of the mill undead and have resistance to edged and piercing weapons.

Ah, yeah, well spotted! As the YT guy says, the blade is shaped like a kukri, the signature weapon of the British Army's Gurkha commandos. Kukris are Nepalese, so I'm not sure if maybe this knife is some indigenous Indonesian design I've never seen before which is used in this "Debus" thing that I've never heard of, but you can confirm for yourself that the inside curve is the sharp bit by watching how he holds the knife during his leaf cutting demonstrations.

Still, it's a funny trick, the kids are having a blast, and if deceptions like this can scare off ISIS, then power to Debus, I guess!

(I was thinking that maybe it's some kind of machete, since the Indo-Malaysian region is well known for its large variety of jungle-clearing machetes, and it would make sense for an Indonesian martial artist to train with one.

It's probably a kukri, though. If you're interested, here's a good video about them by Matt Easton: https://youtu.be/jPSjdj82KLM )

surviving (the other side of) edged weapons