How do I convince my parents that gagging is part of learning in blw?

You can let your parents know that gagging is all part of baby's development. After initial attempts, baby will most likely gag because he either puts too much food into his mouth at once or because he pushes it too far back. Gagging or the gag reflex is a safety mechanism that prevents choking. Baby learns to move food from the back of the throat to the front thus preventing food from getting lodged in his throat. At the same time, he learns what not to do next time.