Things I learned from being an aupair:
I've learned you have to give something in order to get something. An incentive. Kids are impressively smart and cunning and will do anything to get what they want. It sounds crazy, but you have to be smarter than a 5 year old.
You have to realize children will ALWAYS pull the "you're not my mom/dad" card as an excuse not to listen to you. You need to establish authority if you're ever going to stand a chance. Try to state the fact that you're older than them, and that their parents put you in charge while they're gone. The last resort is to say, "Well I could call your mom and see what she has to say about you not cleaning up your mess." That usually does the trick.
I've learned there are many sides to children, and they can flip through them like pages in a book. There's the first page, where they're shy, and excited to meet you. They're not sure what to say, so they run and grab their favorite doll and put it in your lap and then run away (the mom explaining that she must like you since she gave you her favorite dolly).
The second page, where they're more comfortable with you and don't shut up. They will tell you about the girl Maria, who's in their class and who has a pet frog named Jorge. They'll tell you a lot of things that don't really make sense at all, but you just smile and nod and pretend like you care about Jorge the frog.
The next page is where you're just another member of the family. And then you see the bad side of them. You see the screaming and crying and stomping and fit-throwing and door slamming. When you see it for the first time, you experience it second-hand. The parents are there, so you don't have to do anything about it, you just watch. Now that you've witnessed such catastrophe, you start thinking about what set him/her off, and hope to God it won't happen when the parents aren't there to help.
Page four, you are the reason she explodes. You said no more television and turned it off, you told them to finish their milk at breakfast, you stepped on their book that was laying open on the floor, you said it's time to go home from the pool. There's usually no way of talking it through - the screaming is too loud and your voice can't be heard over it anyways. Sometimes (when you're not in public) it is best to ignore it, and let them get over it themselves. Sometimes it helps to just take their mind off whatever it was that set them off. If their pink bracelet snapped while they were stretching it around the door handle (which, inevitably, it was going to snap one way or another), go find the green one and put it on the dolly. This usually catches their attention and they forget about the pink one altogether. Repeat once the green one breaks too.
Page five, she loves you again. I couldn't tell you what you actually did to make her want to be your best friend and follow you around everywhere, but just accept it and appreciate it, because you don't know how long this page will last.
I know just by watching these two little girls for the past two months that time flies. They're not 5 or 7 forever. Sometimes I think that concept is hard to grasp, especially for parents and when graduations rolls around they always say something like "just yesterday it seems like I was teaching you how to ride a bike!" A lot of my own memories from childhood came back to me just from being around them. I'd catch them doing or saying something that I remembered doing or saying when I was their age. Some things seem so important when you're that young, and to adults it's nothing more than a quick decision that we don't think twice about. Like using that sneaky way to be there when their friend asks their mom if you can come over and play, because how can they say no if you're standing right there. And then running and hiding when your parents come to pick you up, because you think if they can't find you, you'll be able to stay.
A side note of being an aupair is that you get close to the parents. They slowly open up to you, and basically become like an aunt and uncle to you. I learned more about the kids and the family this way when I was sharing a bottle of "Tinto de Verano" with mom and dad. This definitely gives you a new perspective when dealing with their children and different ways to approach problems now.
This is also a huge advantage when your living with a family in a foreign country. Chances are you know jack squat about where the closest movie theatre is, or which bus to take to get there. They know a lot about the area you're going to be living at for X months, so use that to your advantage and learn as much as you can.
Even though I was only an aupair for 2 months (compared to people who do it for a year or longer), I learned a lot about responsibility (these aren't your kids, they're someone else's), trust (those parents are entrusting you with their children), and kids in general (some are more stubborn than others). I'm not sure if I want to do this again more summers in different locations, but now I know what to expect if I do.