Just as a side note here, make absolutely certain that they never, ever bring them to school. I used to carry a little lockback when I was 13, and I got "caught" with it (I didn't think of it as a big deal, but the school administrators sure did). I was suspended for a week and put on 6 months of informal probation. I had to put on an orange vest and clean up trash with the gang member kids. All cause I carried a 2.5" lockback.
And no, I didn't threaten anyone with it or anything, no would I ever have intended to. It just fell out of my pocket in front of the teacher.
Excellent advice.
I don't know how you give a child a special present and then tell her not to bring it to school or even show it to her friends (who might mention at school that your daughter has a knife -- and that in itself can be enough to get her into trouble.)