In surveys, Orthodox Jewish women rate their happiness with life higher than secular women. You could argue that this is subjective, but I think you would find the same if you look at other derived markers, like substance abuse, suicide, etc.

There can be multiple reasons why modern societies have less kids, but the main theme of Orthodoxy is to keep as much as possible the same as in previous generations. So they would be avoiding almost all the possible reasons given for the decline.