It appears like your youngsters are coping with a kids’s account that forestalls the addition of reward playing cards from the account. I feel you would need to add the reward playing cards when logged into your account as an alternative of the youngsters’s account. Failing that choice it’d imply altering the kid account to a full entry account and that will take away the parental controls you at present have.
A minimum of that will be my ideas based mostly off the display screen you will have shared up.