I found this information in the cruise planner but I'm not sure how this applies to Izumi tbh.
[For Cover Charge Products], Children between the ages of 0-5 are complimentary and ages 6-12 are $10 per child; children must order from the kids menu. Please reserve product for all guests who wish to dine. Adult price will be applied for all guests regardless of age; the difference between the adult price and child price will be refunded in the form of a refundable onboard credit (unless booked with non-refundable credit, in which case OBC will be non-refundable). For Dining Packages, children ages 12 and under are excluded from offer.
I hope that helps!