Jenny,
There are several sides to this thread, first is the obvious one that they may have never seen a CDer before , they won't act like that alone but with a group it's so predictable a group of young girls will be vocal about it . The next point many of that age might have brothers , boyfriends etc and that age many associations might be sexual if they caught them wearing female items . ( I know this one from experience !) Another point is they are possibly too young to grasp what CDing and being TG actually means .
I would doubt it's a reaction in a detrimental way , it's possibly a new experience and something they will have to come to terms with in this modern generation . If they go into sales or sevice industries they will be trained to deal with these situations . I have to admit a young girl serving me in a tool store yesterday did get a fit of giggles , the SA standing next to me had served me before so she was trying to settle her down , I didn't have a problem with it she has to learn how to deal with people as we all did at some point .