You did not specified what the traumatic experience was. A kid of 2 to 3 years has many reasons for such a behaviour. Maybe the kid could be missing parents while at school, psychologically speaking some fixation during infant stage etc. This can be really handled by a dedicated teacher like you. Have loads of patience and you don't get emotional or anxious. Think of practical ways of handling the kid. Maybe seek your seniors or experienced teachers for help.
Not sure how the parents are handling the kid at home, is there a new arrival in their family, many reasons to be analysed.
Next Steps
let the parents consult Psychologist, if they are okay to do so. There are positive Counselling to help, many of them think Counselling is only for problems. Discuss with the parents, leave the choice to them. You can be instrumental to help, mind your emotions as you have a life and family of yours