Have a look at gohenry.co.uk. Its a debit card which you (or anyone) can pre-pay money on to. It works the same as any Visa debit card, so they can withdraw from cash machines, use in shops etc, same as your cards. They can manage their account online or on an app, it has a savings account facility so they can transfer cash from the current a/c to there, view their spending etc.
As the parent, you have a slightly different app, which manages their access, plus lets you add money. You can also set daily/weekly/monthly targets i.e household chores, homework done...which must be achieved before the next lot of money is released if you want.
We've just set it up for our kids. We have a d/d set up to be paid in every Friday to each of their accounts. So far, they've gone and withdrawn some of the money so they both have cash for holiday sweets etc. One has something in mind to save up for, and is planning to use the savings facility. At the moment we've not set targets as we've seeing how it goes, but we have discussed household chores and homework which needs doing, so will review it once they're back at school.
The main thing I like about it is the app, it's tapping into their existing use of technology in a familiar way, and gives them a degree of independence and choice, without having to discuss it with us first. The money paid in is finite, they know what we will and won't pay for from now on (mainly ad hoc sweets and treats!), so it's their to do with as they want.