If they do their jobs right, they won't have to bowdlerize anything.
There's really precious little in the way of cursing in Japanese; much of it is largely contextual. There are certainly some words which are impolite in any context, but by and large it's largely a matter of how far in the gutter the translator's mind is. The truly demented could theoretically turn even the most innocuous kids' show into something that would make Eric Cartman blush.
Try "kuso", for one. Literally it means "feces" or "excrement"; think of it as a catch-all for every four-letter English interjection from "darn!" straight up to f-bombs. That's right, it's an all-ages curse, but only the most deranged translator would have a little kid dropping the f-word (or, from the opposite perspective, a grown man who's just seen his hometown nuked and his girlfriend raped and mutilated by mutant cyborgs shouting "darn it to heck!"). Context is the key.