Middle Ages (AD 476 to 1454): Even though it has magic, we take Camelot to be in the real middle ages, but we also mark it as being debatable time travel.
Unspecified Year: The time travel is debatable because the kids go to a land of magic. We need to check whether the land is explicitly set in a particular time period.
Timeline Models
Single Static Timeline: Within the series, anything the kids do seems to fit known history rather than change it.
From the magic tree house in Frog Creek, Pennsylvania, circa 2019 ⋙ to a mythical land of sea serpents at an unknown time. Round trip. Note: The mythical land is most likely not in our timeline.