Children need more of a reason to do things than "Because I said so" or "Just because." Give them a *good* reason, and they're far more likely to cooperate. Give a good enough reason, they'll help you willingly. Even something as simple as "Because I work hard and that work stresses me out, so helping me out would be a huge relief," or "because there are things we have to do even when we don't want to, because they need to be done," or something to that effect. That kind of answer encourages kids to be helpful and kind. The "because I said so" sort of stuff just encourages kids to get resentful and rebellious. Expecting a child to do something just because you - the adult - says so is disrespectful. You can't disrespect someone and expect respect in return.
Remember, children are new to this world. Just because YOU have all the social rules, expectations, and nuances of life figured out doesn't mean they do. They don't know these things! What is obvious to you, as an adult, is often not even on your child's radar screen. Your job as a parent/guardian/teacher/what have you is to teach
them. You can't teach them how to read by expecting them to already know how to do it, and then yelling at them or spanking them when they show you they can't, so why should the rules of life in society be any different? If you can't be patient and kind, and if you can't be respectful toward your children, you shouldn't be having any.
EDITED TO ADD: A bit from kengr
= Oh, further thought on the adult vs kid stuff:
1. keep in mind that if there weren't *explicit* rules against what the kid did, it's likely not remotely fair to punish hir for doing whatever it was. Just because it's obvious to *you* that it was a no-no, doesn't mean it is to the kid. You may have to suck it up and accept that *you* screwed up by not telling them not to do that.
2. If you make a deal with a kid, you'd better have a *damn* good reason for breaking it. And you'd better be prepared to offer reparations if the deal involved the kid doing something for you first.
My response: Amen to both of those. My dad made the mistake of breaking a number of promises made to Tara (my younger sister). Too many. They don't get along well at all anymore.
Crossposted from http://fayanora.dreamwidth.org