We were all young once and to be perfectly honest, if you had sat me in an aircraft at age 13 with a flying instructor I would've been hard pushed to focus any attention on the exercise in hand other than worrying about my life. For some youngsters it sits well, with others they couldn't care less.... it's part and parcel of being an instructor which you just get used to. The sooner you realise that you aren't going to be the defining factor as to whether they love it or hate it the sooner you start to relax and enjoy the flying yourself. You will never be able to impart your love of flying on to a disinterested youngster (or adult for that matter), it has to come from within the individual.
VFE.