I think there's another side to this actually.
Yes as a teacher, get a CRB check. (As a parent, understand that £xx only buys £xx's worth of checking.)
But as a teacher, it is much more important to appreciate that children will trust and look up to you, and if they are being hurt by someone else, you owe it to them to notice. And to inform yourself about how to react, what to do if a child comes to you for help, because it is not obvious, and the wrong behaviours from you in that situation can potentially scupper any chance of justice being done.

It seems to me child protection education is far too narrow at present - a lot of it is limited to the panicky 'don't touch that child - s/he'll sue!' message. Which is actually not child protection at all...