as my husband always has 飛滋 and my son (4 years old) seem to have same problem (he has twice before but me and my daughter get no problem), i consulted my doctor and also according to some articles, what i could share is:
飛滋 is hardly defined if it is a inherited disease. however, once you get your 1st 飛滋, it's very easy to get another and another one in the future. so we have to brush teeth twice and completely everyday and be careful if there is any wound in your mouth as the wound will become 飛滋. vitamin b2 is a good supplement but iit's not common in the market (at least those big brand like "doctor's choice" or "century" don't have) Also, it is better to have the little kid get the vitamin naturally, i suggest giving some animal's inside, e.g. pig's liver, chicken liver. even my friend takes vitamin B complex instead of simply B2, she said she gets less 飛滋.
Try to use Comvita's Proplois Toothpaste (Can find at Comvita's shop @4x.-) Is good for kid and my
son use it almost 2 Year and less chance to get
"fay Chi".