What's acceptable and what isn't?
My DH thinks it's fine for our 3yo to shout "oh knickers!" and "oh pooey!" and that sort of thing, because it's not really swearing. My point is that whilst it's not particularly offensive to us, parents of other children at pre-school may not be so amused with their DCs learning and repeating it. Also I suspect that the teachers would probably pick them up on it too, which is embarrassing and not very nice for them. DH thinks I'm just being stupid, but I don't think it sounds very nice.
Am I old fashioned and worrying too much, or is "oh dear" as far as it should go when you're 3?! (I'm fully aware that before too many more years, they'll probably be teaching me some new swear words anyway )