[googlryas]

Just my own observation, but all the kids I remember that cursed a lot weren't very good at English. Not sure if it is correlation or causation, but who needs to find the right word to express yourself, when "fuck" or "shit" almost certainly fit the bill?

Maybe people who curse poetically are even better at English than non-cursers, but that probably comes with age and isn't relevant to advice about children.

[khazhoux]

My anecdata is similar, but rather: the little kids I know who curse a lot and openly, have terrible manners overall. Talking nasty to grownups (and other kids), etc.