I believe the "OnClicked" will only work if it is a CT_BUTTON. Beyond that, you'll probably have to wait for someone more experienced to see this. I have not needed to use handlers that required parameters to be passed along yet, so not sure if there's anything else wrong with that. Otherwise the code looks right.
Edit: also, I'm not sure if the syntax is correct unless you're calling a global function, but it might need addonName or self for
Code:
child:SetHandler("OnClicked", function(self) addonName:BBS_SearchBoxOnTextChanged(bbs.editbox) end)