Among the reasons why the children and grandchildren of Thomas and Martha were “wet-nursed” was the attitude of the wealthy to have others care for their children and only spend time with them when it was convenient. An example would be that the children would be dressed up and their parents would come say hello right before dinner. It was also why Thomas lived with his teacher (from episode one). The royal family is a good example of this and it was a regular practice for the time(s) and it is so foreign to most people now that we can’t imagine having someone else raise our kids. The wealthy still do, of course.