My sil and bil are buying a new car soon. Mil mentioned to us that they were planning on forward facing their son in this new car(unsure of why) He is only 4mths weighs about 9kg. They seem to think that it goes by weight and he is right to switch but I thought it now goes by age. This is their first child and they don't seem to listen to much of what others tell them. Even mil doesn't understand why it isn't safe to turn him yet. Any ideas on how to tell them with offending them. DF and I are concerned about his safety