The statement "In this house, children are supposed to be in bed by ten o'clock" suggests an expectation or requirement regarding the time children should go to bed. Option D, "not later than," is the most appropriate choice because it conveys a similar meaning to "by ten o'clock." It implies that the specified time is the latest allowed, and going to bed after that time is not acceptable. Options A, B, and C do not accurately capture the idea of a specific time limit by which the children are expected to be in bed.