happiness is related to the society you live in and your biology ... and other variables. its entirely possible that you can be both "objectively worse off/more stressed", which is generally considered to be a cause for unhappiness and still feel that the children were the best decision of your life.

its a complex topic and i dont think anyone can realistically generalize it.

there will be people that are actually unhappy because of them while still claiming happiness, as well as people that were unhappy until they finally had them.