Tacky. I think that it is rude when your server brings your check out when you are still eating. You should request your check and it should never be tossed on the table no matter how discreetly. There have been times when I was contemplating getting a dessert and decided not to because I got my check just after my main course without my request. Of course, if I really want a dessert, I will get one regardless. Still I find that most times I'm in between deciding the "should I?" or "shouldn't I?"
Just wanted to add that not all young couples with small children are bad tippers and if you ever see me and my too generous husband, it would be great if you give us great service, because we notice and will tip greatness with great $$. We always tip just better than 20%. The lousiest service we get still gets 10-15%, but it ranges, because tipping lousy servers good is a disservice to great servers. Be polite, smile, don't try too hard with the small talk--respect that I am out with my husband and kids and not you, bring timely refills, fix any "bad" or "wrong" orders, don't forget we exist, give me a decent table away from the kitchen/bathroom (I love windows or areas that are "tucked away"), and don't bring me my check until my dh asks for it, and everyone leaves happy. Now, since you don't know what I look like, remember not all young couples with children are bad tippers--but if you are smart enough, you might see signs that I'm in your restaurant. My children are well behaved, decently dressed and my husband and I are well-groomed, have proper manners and tend to be well-spoken.