"Amma" means mother, "magan" usually means son, but in Tamil family terms, it can also mean "my son" when addressing. "Thagatha" could be past participle of "taga" which means to steal or snatch. "Uravu" is a form of "iravu", which means sleep or rest. "Kathaigal" is stories or tales. So putting it all together, maybe something like "Stories about a mother who stole sleep".