I can find no reference anywhere to police checks on characters and I'm not suprised really.
Even if they do seeing that the majorité of these people are late teens unless they had commited a major offense (for which they would be still locked up for) their charge sheet would be wiped clean at 18 so it would come back clear.
There are a lot of differences between the 2 countries now that the UK has become strict.
You only have to look at the school trips/days out to see the difference. Here you will see 2 adults with 20-25 children of primary school age, they don't wear hi-vis, travel without seatbelts in coaches, can be taken in groups in teachers/parents cars
Parents can go along to help out at events without having any controls made.
Look at the groups in DLP this summer you will see teens looking after groups of children that have come from the North of France for a day out organised by the town.
(You see a lot of this in the holidays and last year OH and I were infact shocked by one group as the teens were smoking and shouting at the kids)
The characters are never left on their own with the children and they are costumed up completely so I would have thought that a risk of any mal intent would be extremely rare.
I guess I was more suprised to learn that the characters were interchangeable - The person in Minnie could also be later in Mickey and then later a Princess for example.
ps-I've just checked with a friend who is a babysitter through an agency. She has never been police checked and goes daily to peoples homes and looks after their children.

Wasn't sure were smilies were appropriate in the above so I'll wish you all a great day here at the end
