I think they are only out of school because they have kept them out of school to shelter them on purpose, not because there schools aren't in session. Winter break for there age group in the US typically end Jan 2. So they would have been in school the entire length of her trip. When she went missing , I think they pulled the kids from school to shield them.
I think you misunderstood, I was saying she might not have wanted to go in the summer because in the summer the kids would be out of school and need more times and attention. (This was before the talk of them being homeschooled came up.)