Regarding to your inquiry, we regret to inform that we are unable to reserve the amount in the booking due to system not allowed.
On another note, infants can be bring on a flight; you will be subjected to the infant fee and you may check the fees through this link http://www.airasia.com/my/en/where-we-fly/flight-schedule.page?
Since infants are not allocated seats as they travel on an adult's lap. However, we allow baby buggies/strollers/prams to be carried free of charge.