A friend from high school joined a very conservative Latino church in our area after high school. They don't celebrate birthdays, Christmas, Halloween..etc. But I don't believe they're JW, just a very conservative Protestant church.
My mom is a preschool teacher and will occasionally have someone in her class who doesn't celebrate birthdays or halloween. It's sad because they have to go into another room by themselves (with an teachers aide) during the halloween party and don't have their birthday acknowledged even though all the other kids do.