Just out of interest I am wondering what "bad" behaviour you let your children get away with ??
What I mean is that my MIL thinks its very terrible that sometimes my boys (2.5yo and 4yo) sometimes resort to silly language between themselves and start saying "willy, poohead etc etc" to each other and us all. MIL is very prudish in the extreme and regards any talk mentioning genital parts etc as inappropriate. Whereas I on the other hand am not particularly bothered by this sort of thing and think its just a stage and there are bigger battles to be fought than that sort of thing.
What doesn't bother you in terms of behaviour that may bother others ?