This is a great idea! It’s not often I’m enthusiastic about a new product from a bank, but if my kids were still actually children, I’d be all over this.
When my younger daughter was a senior in high school, I put her on one of my credit cards as an authorized user because she was going on an interstate trip with friends for the first time and I wanted to be sure she’d be covered in an emergency. Luckily, she was the kind of teenager you could trust with money. She still has that card - when she was in college, she’d use it (with prior notice) to buy things online before she qualified for a card of her own, and she always transferred the money to me afterwards. Now she uses it to do my shopping when I’m lazy.