That seems like it would be ridiculously problematic. What if you weren't married to your child's father and you gave the child his last name (which my mother did)? Or you divorce your child's father and want to return to your maiden name or get remarried?
For kids (at least in this state) you can't be the one to enroll them in school, take them in to get a drivers license or passport, or in some cases dictate medical care when you don't have the same last name. That's the main reason mine is changing (also because it was something important to my husband).
My bratty cats are driving me crazy. Ruby and Carrot keep getting into little scuffles for no apparent reason. At breakfast this morning, Carrot jumped up to the counter they ate at a different way than normal and scared Ruby so she upset the water dish and everyone ended up soaking wet. Then during their second meal, Carrot glared at her (which he does sometimes when he finishes food and others are still eating), she totally was set off hissing and growling at him. I had to scruff her so she didn't bite me when I grabbed her to stop her jumping on him. So frustrating!