As a child I was an unaccompanied minor on British Midland, and was invited to spend the whole flight from LHR to EDI in the jump seat of a 737. As you can imagine, they didn’t have to ask me twice! On another occasion, I visited the cockpit at dawn during a night flight over Africa on an Air Zimbabwe 707 (I think - I was very young).
Although it sadly isn’t possibly to do that these days, even the on-the-ground experience of going into the cockpit and a friendly crew really does make for an unforgettable experience for impressionable youngsters. Although there is sometimes a lot of moaning about BA crew on here, I think they are generally very good at looking after younger passengers in this way.