Hi Twinsmammie,
I am not sure about their other classes, but for the 2 classes (Montessori and Creative Writing) that my sons are enrolled in, there are no additional charges besides course fee.
They have trial classes for some of the classes, but I am not sure that include the montessori classes or not.
Why don't you talk to Josephine directly? She is the owner and she is a sweetheart. When she is not busy, I could chat with her forever on kids and education. See the thing is, if you ask a nanny to bring your kid there, you probably won't get a trial class. But if you could bring your kid there yourself, I think it won't take you much effort to get a trial class. She is very nice to talk to.
My sons rarely miss classes there, and for the time that we missed, it was problem free. They are quite understanding. For example, at one point, my girl freind wanted my 2 yr old to go to COW more often so our sons could attend montessori together. I tried a couple of weeks and felt that my 2 yr old wasn't ready. I told Josephine that I wanted to take it slowly. And I am now back to normal. She was very understanding, and was not pushy at all. I am quite happy with their quality and attitude.
Hope this helps. =)