How to label his clothes without ruining them?

our 4 year old is about to go to school from 6th April, for a couple of days this month so that they get used to the environment, the school wants his name on his clothes (shirts and pants), and I’m a little nervous about messing them up. How do I do it without ruining the fabric? I want something that’ll still keep the clothes looking nice. Do you write directly, use labels, stamps…? What’s worked best for you?