Revolut <18 card and Child Apple family account

I have set up my children’s Apple account and added to my family to manage my kids screen time. I have also set up revolut u18 for my children. Why am I not allowed to add a card to my child apple wallet? The block is on Apple saying the card is not allowed to be added for u16s even though it is me as an adult trying to set this up for my kids to make life easier. The kids have lost so many cards but they don’t lose the phone!! Can this be reviewed to see how it works for Apple Pay as it works for google pay fine