Quote little sage
Yes, I always do name tags, even with adult classes (though I don't make the adults wear the tags).
I precut paper and fold it, teach the correct romanization of the letters (in Korea, it's the vowels that are killers) and have everyone write their name on the sheet and stand it on their desks. At the end of class for the first few lessons (OK, many lessons) I collect their tags and then use them when I call roll next lesson. I also group the tags into clusters of who sits together and that also gives me a way to remember who's who. With classes of 30+ that meet once a week, it takes some time.
For kids, I let them use colour and maybe draw something on the tag that they really like. Then I have a visual image to go with their name and their face. That helps me remember.
I used to have the kids write their names, but I found that especially with the little ones I couldn't read the card from the front of the classroom. I know it sacrifices the chance to have them practice the romanization, but I think it's more important to be able to reliably call them all by name. I print labels of their names off of the computer and let the kids decorate around it. And it works! I have over 400 regular students and I can call almost all of them by name even without the cards, now.
Since I've been at the same school for so long, the only new classes I ever have are incoming first years. I usually do simple games that they know already, like Janken Train, and a circle introduction activity where everyone says "My name is ..."