I have a 4 1/2 year old and a 1 1/2 year old.
I'm a terrible curser, I curse casually all the time.
To me it's just another adjective.
My Parents curse casually now, but when I was a child, I don't remember them using quite the same language, quite as casually.
When we all grew up (teenage years) it was not a big deal to curse casually, but god help you if you cursed at somebody in anger- that was not tolerated.
You could curse to joke, or make fun, or in the midst of a conversation- but in an arguement, no.
To date, my children don't curse, (I did once see my eldest roll her eyes and say oh, for f*ck sake, once, but she was'nt saying it to be naughty, or directing it at anyone- plus, it was a fantastic appropriation of context, so I let it go)
I won't be surprised if they did drop one in from time to time, but it would just be a word to them, they don't see us cursing in anger, so they don't use it in tantrums or whatever. Our job will be to teach them that there are time and place appropriate language and behaviours of all different types, and what's appropriate and where.
There is also zero reaction when an adult curses in our house there's now shocked intake of breath, or people trying to cover it up or "not in front of the children" comments- so they don't get the impression it's a "naughty" word to be dusted off and used for effect later at all.