Actually, for us it was the opposite ... when DD came into our lives we realized (or at least hoped) she'd be our last one. While with the "first round children", hubby and I both worked and put them in daycare, shopped only at thrift store and were super-frugal and super-organized (and super-strict), with this one we wanted to do things differently. We both made moves to be home more. We refuse to put her in daycare (unless absolutely unavoidable) and we are definitely more relaxed. Because she is being raised as an "only" we tend to treat her more and spend a little more on her.
I can say, the biggest financial change over the years has been cash. When hubby and I were newlyweds, we could withdraw a $20 bill out of the bank and that would last us an entire weekend of fun. Those days are long gone. Now we withdraw a $20 out of the bank and stay home - LOL!