Language Lafda - Naisha

Okay this Hindi English thing is terribly confusing... The other day mama told me to keep quiet and go to sleep but I wanted to sing a rhyme with her so I said 'Naisha ko singna hai' and sent mama into fits of laughter. Then there was the time when I said 'Mujhe sitna hai'. I mean how is one supposed to figure out which is a hindi word and which is an English one? Words should come with labels. Mama keeps talking half in Hindi and half in English... how am I supposed to figure out which is which?????