You can check in a baby stroller or a child seat of your child travelling together without charge.
In case your child is not using a baby stroller or child seat, these items must be checked in with the fee as checked baggage.
Please check the link below about fees and charges.
「Fees and Charges」
REFERENCE
If your baby stroller or child seat is within the the limit, it is allowed to be carried on.
Please see below for more information on the size restrictions.
「I would like to know the size, weight and the number of pieces of baggage that I can carry on board.」