Captain Defenestrator

Question: In 700 years, everyone on board the Axiom has grown very fat, lived their whole life on hover chairs and kept their faces buried in their screens. So where did all of the children come from? Every adult only looked at or talked to each other through the screens so how could any children exists if the adults never left the hover chair. That kind of ongoing lifestyle should not have produced any children at all and after about 200 or even 300 years all life aboard the Axiom and other ships should have been wiped out.