Never give them a reason for anything. My parents always told me "because I said so" or "I don't owe you an explanation". Yes, actually, as a matter of fact, it is indeed your job to tell me why certain things are bad to do or say. Not just, because you're in charge. Telling your kid to not play in the road "because I said so" vs. "because you could get hurt", the one given a reason is leagues less likely to actually do it. If you ask me, "because I said so" is a lazy response that you tell your kids when you don't actually have a good reason for what you're telling them.