Hello everyone, thank you very much for your answers. It really helped me to deal with this situation (instead of just hiding under a stone and never going back there again.)
What happened so far: my supervisor at the place wrote me an email asking what happened and if I still wanted to come. I wrote back and apologized for my behavior. I also tried to call interngirl, but it probably was too little, too late and she didn’t answer. So I apologized via textmessage. We had a long summer break and a new volunteer will work alongside with me once we start again. I decided to give this another try. The only ones I haven’t talked to yet are the kids who were there that day. I think the adult thing to do would be to talk to them, too, but that might get really awkward. I come from a family with a long history of “just pretending it never happend” when it comes to wrong behavior, so actually apologizing is really difficult for me.

Anita, I will try your suggestion next time, thank you. It sounds simple but effective.

Jan T, you are right, I probably need to involve myself more to feel involved. I can be shy at times and sometimes it can be overwhelming. As for how to treat the kids, it’s daunting because I couldn’t even deal with them when I was a kid myself. Now I’m older, maybe wiser, but not sure if I can keep up with them. Maybe I should get a book on the topic, as you suggested.

Sann, no worries, your post made perfect sense even if you were tired. I too have followed those avoidance patterns, so what you wrote encouraged me to try again as good as I can and maybe learn something from the experience, too.

Bethany, I’m not sure if I saw the intern as a thread. Rather I was really frustrated that she didn’t (magically) understand that I really wanted to do my cake and not her boring chocolate cake.
When I say I don’t deal well with children I guess I mean that I’m not very funny or interesting. I’m afraid the kids just won’t come anymore because I don’t do a good job. I also think that kids are smart and will quickly know when you are saying stupid stuff and call you out on it. And I for one have a history of saying stupid stuff in the heat of the moment.