I speak Thai constantly every day because I work at a bilingual kindergarten that leans much more towards Thai than English and I'm the only native English speaker. There are some other English teachers, but English is their second language so they lack confidence and don't really know how to manage or just casually speak with the kids in English outside of lesson time.
When I'm teaching regular lessons I use pictures, songs and TPR to keep it immersive, so once the students have learned their basic classroom commands I speak almost entirely English. But outside of lesson time, when I'm carrying kids throwing tantrums into school in the morning, calming kids down so they can sleep at naptime, talking to their parents about what they did that day when sending them home or explaining things throughout the day to coworkers, I do it mostly in Thai or kind of flip/flop between languages.
Admin wants me teaching the other teachers English, but if I speak only English to them they do that Thai thing where they just smile and nod and I can't tell if they understand what I'm saying or not. So usually I'll speak English and then repeat myself in Thai if they don't say anything.
I do the reverse when I'm casually speaking to the kids outside of class. I have a pretty good understanding of what English the kids do and don't know so I can mostly stick to English, but if I'm communicating something they haven't learned I'll say it in Thai once and then repeat it multiple times in English. I'll also translate things I hear the kids saying in Thai into English, which usually gets them excited and shouting new English phrases at their friends.
I've also had students who used to go to international schools, but were switched to my school because their parents don't know much English and were worried their kids wouldn't be able to speak Thai at all. The kids are so excited when they start coming to a school where they actually understand what people are saying to them, and they love talking to me because I'm the only farang they've ever met who understands them when they're speaking Thai.
I had this one student who would keep testing me to see if I would respond to things he was saying or not in Thai and then yell my name and hug me. After about a week of this he started speaking to me only in English and excitedly repeating all the new English words I would teach him. He liked speaking English, but liked the security of knowing he could speak Thai as well if he needed to.
A large part of kindergarten is relationship building. The kids need to love and feel safe with you in order to respect and listen to you. It's hard to do that when you're a tall, pale alien ignoring everything they say and making strange noises they don't understand.
Kindy TEFL Teacher