Dave - thanks, good stuff. The kids keep insisting we take them to an endocrynologist and forget all this "natural fennel seed" junk that's getting us nowhere.. This is helpful ammunition.
I'm sure anything a doctor would do to (try to) help with their hormones before the SIBO stuff is under control would only do harm.
Since the kids used to eat lots of sushi (and not always from the best sources) I've always thought parasites had something to do with this too. Unfortunately when the doctor says there's no evidence of parasites, it was hard to keep them on a parasite cleanse - especially when it caused lots of extra gut discomfort.
I'll check on a good vitamin C. I also took another posters suggestion and ordered Betaine HCI just in case low stomach acid plays a part - since stomach acid is important as a defense against bacteria in the small intestine.