I think it might depend on how stubborn a kid is: I would suggest explaining your reasons for your suggestions. Since they are younger, they are most likely open to your suggestions if you can communicate clearly the pro's and con's of one actions.
If they are not willing to accept your reasoning, you have to be a little more harsh and put them in a situation that condones your reasoning. The reason that people (not only kids) act rich and spoiled is because they are in their comfort zone. Once your remove them from that comfort zone and remove all the power they think they have - you're on the upperhand. It is at this point when they are most susceptible to suggestion. At this point, you must also be a guide for them. You have to be clear on what you're trying to express to them. Don't confuse them with the theory, instead, use "cause and effect" examples.
I don't have any kids of my own, however, I work with kids and stubborn people on a daily basis.

- Sam