I have sometimes wondered if dinosaurs evolved FROM mammals,for the simple reason that many types of dinosaurs incorporated mammalian features. I suspect that many types of dinosaur had a physiology that allowed their bodies to regulate blood temperature similar to a mammal. Some dinosaurs gave birth to live young after a period of gestation within a womb. There are many other similarities too which I guess you are aware of.
This is a case of parallel evolution. Remember, mammals evolved from reptiles, just as dinosaurs did, and they share many traits. However, there are clear distinctions between mammals and dinosaurs, particularly in their bone structures, which look nothing alike. Furthermore, the earliest confirmed mammals date from the late triassic or early Jurrasic period, millions of years after dinosaurs. Lastly, it makes little sense that a reptile would evolve into a mammal and then back into a reptile before becoming a bird.
As for the warm/cold blooded debate, the prevailing theory is that dinosaurs were dinosaur-blooded. They could regulate their body temperature to some degree, but still relied upon external heating and cooling somewhat. Some dinosaurs (dromaosaurs) may have been truly warm-blooded, but most were somewhere in a transitionary state between the two.
And yes, some dinosaurs gave birth to live young, but so do some reptiles - rattlesnakes spring readily to mind. Most dinosaurs laid eggs. Virtually all mammals give birth to live young. Furthermore, almost all mammals have mammary glands, and there is no evidence that any dinosaurs possessed this adaptation.