I do have children, and handling real money was an important part of them learning the meaning of money. They also use contactless (where available through their banks), and receive their pocket money online. However, asking them to use a contactless card for ticketing raises a number of issues in my mind, and I would certainly be reluctant as a parent to authorise it. The two key ones are ensuring that they have enough money on their account for their travel (remember, the child purchases the tickets in this scenario, not the parent), and the security of a minor using their payment card.Eh? Children have always been allowed to have bank accounts. "Back in the day" they were typically passbook based (I think I got a first cash card aged 13, which is early 1990s) but now they're not, and you've got things like GoHenry for younger children.
This might have been a reason in 1985, but it isn't even close to being one now.
I don't have kids, but if I did I would be far, far happier with them carrying a card around (which I could easily block if they had got into trouble, e.g. other children were trying to steal money, or I suspected they were up to no good) than cash, and no chance of spending it on drugs/alcohol from other children. Being an IT-oriented person I used to save up for various bits of hardware, and recall my parents being quite nervous at the idea of me drawing out say £250 cash (probably the equivalent of a grand now) and walking down the street with it in my pocket.
Thinking of group outings they've done, or I’ve been involved with as a helper, this would engage significant safeguarding concern.