Having spent the last 12 years working in schools, both primary and secondary, I can assure you that what they hear at a footy match is no worse that what they hear and use in the playground, both to each other and to members of staff.
In an ideal world we would all like to shelter our kids from bad language and the likes, but the fact of the matter is, the kids are often the worst perpetrators, and yes, I do mean the 5,6,7 year olds.
I can only assume that they have picked it up from home from parents who swear openly in front of their kids. This new found vocabulary is then practiced and extended once the kids are out and about with other kids.
Unfortunately, the very people who are trying to protect our children, have, as is the norm in these cases, gone too far, because as no-one is allowed to discipline kids any more, they are able to get away with it and, along with vandalism, graffiti and a whole host of other anti-social activities, becomes the norm within a certain section of our society which is then copied by their peers, who don't want to be seen to be different.