hello and welcome to hcm forum,
i would like to inform you that a child as young as 2.5 years should not be asked to use listerine
or any such oral hygiene
products due to the risk of getting ingested, which can lead to serious medical complications.
therefore, stop using listerine, brushing teeth twice daily is more than enough for a child.
you can brush your child's teeth with a soft bristle brush, do not use tooth paste more than 2 times in a day and the amount of paste should be pea size.
or rinse mouth with plain water.
if the problem still persists then kindly visit your dentist
i wish you good health.