I booked one with CX that turned out well (though had to be booked over the phone). Initially we booked a seat for the infant but later cancelled it when they changed the seating config to herringbone.
I have booked Int J any seat award (and Dom J and Int Y) online for an infant with no troubles. I think only requisite is that there are less infants than adults.
You can also book an award seat for an infant over the phone, they simply select "child" and then put the real DOB. As I had to book so far out I thought 8 hours on the knee would be fine. As the trip grew closer (and the child bigger and more "independent") I chickened out, and rung QF who released a classic award seat for Sequel Inf.
Tried last week to book a (child) seat for a infant on MH, however the website tripped up over the DOB being infant. Rung MH who said just to book as a child and enter an eligble DOB, then simply ring MH to change the DOB.
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