1) Mixes of hydrogen and oxygen are highly explosive 2) Hydrogen tends to leak with ease even from metal containers (hydrogen molecules are the smallest). 3) There is a tradition to use lighted candles at birthday parties. 1 + 2 + 3 makes for a disturbing (although admittedly fun) combination.

https://www.youtube.com/watch?v=ce6imsXTkGQ

Doesn't seem to be too much of a risk, judging by the videos. (Not more than giving kids knifes to cut their steaks. Or letting them carve wood.)

PS Thanks for the video!