Let p(t) be the percentage of children that are male at the end of year t. How is this % expected to evolve through time?

Question

A mythical city contains 100k married couples but no children. Each family wishes to 'continue the male line,' but they do not wish to over populate. So, each family has one baby per annum until the arrival of the first boy. For example, if (at some future date) a family has five children, then it must be either that they are all girls, and another child is planned, or that there are four girls and one boy, and no more children are planned. Assume that children are equally likely to be born male or female.
Let p(t) be the percentage of children that are male at the end of year t. How is this percentage expected to evolve through time?

Answer 1

When are the children going to have children themselves? Are things like incest considered? Or can we just expect everyone to find an adequate partner?

Answer 2

Well! You can consider the incest case. But do not count those children in p(t). And also forget about the grand children.