That is exactly what we did with our infant son. Traveled LAX-ICN-LAX. Paid 10% in Prestige and was able to take him with us. Our son was not assigned a seat in Prestige but the agent on the phone told us to book a flight we thought would be relatively empty and they would be able to assign seating at the gate for him. We ended up booking seats 11D and 11F on a Wednesday evening flight and sure enough, Prestige was 1/2 empty. The gate agent assigned our son 11E and off we went.