2 year old is the threshold between a child and infant ticket.

Below 2 - Infant fare. No seat provided, only bassinet. 10% of full fare + taxes. No award redemption available.

Above 2 - Child ticket. 70% of full fare + taxes. Award redemption at the same rate as adults.

If your child crosses the 2 year old mark during the travels, the entire ticket is considered a child fare.