Thank you. / Thank you for everything.
The Japanese phrases above are shown in increasingly formal order. If you have just entered the preschool, if you are writing or speaking to a teacher who is significantly older than you, or if you are approaching a teacher with a concern or a request, you may wish to use one of the more formal phrases.
However, always using formal phrases makes it difficult to develop a sense of friendly familiarity with others. For this reason, you may choose to use casual greetings such as 「おはようございます」(ohayo gozaimasu, or "good morning") on a daily basis, and save more formal phrases such as 「お世話様せわさまです」(osewa-sama desu) or 「お世話せわになっています」(osewa ni natte imasu) for times when you wish to talk about a concern, make a request, or express your gratitude.