I never, ever send my child without money. I usually give it to the parents because I know my DS will make unwise choices if given the opportunity.
I kind of view it this way: Im training him to be an adult. As a parent, thats my job. If a friend invites my kids somewhere, and my child is trained to think of his way is then paid, why should it be any different as he gets older and parents are taken out of the equation (i.e., high school, college, adult life)? Whenever one of my boys and his buddies get together, if a friend initiated catching a movie, should my kids think someone else is going to cover them? Or, if one of my boys invite a friend to go bowling, should my son be expected to cover the cost of his friend?
Im the kind of parent that starts teaching my child not to talk during the movies or how to hold a fork properly from the beginning (not that I expect 100% compliance) because I figure that kids dont turn some magical age and suddenly get it. If they start right from the beginning, theyll get it faster and easier; it will be second nature, if you will. And I pretty much follow that theory with everything.
Sometimes my kids come back with the money, most of the time they do not.
As far as paying for my kids friends, it depends. I dont ask for money and will most certainly cover the child in anything we do if none is sent. Same goes if not enough was sent. If we decide to do anything extra than what was originally planned (stopping for ice cream on the way home for example), I cover the child. Ill often treat to the minor things, like snacks, even if sufficient funds were sent. If we are doing something a little on the special side, like a play, that requires purchasing tickets in advance, Ill pay. I also usually preference the invite with my treat or well cover x, y and z. If we just invite them to go out for pizza or something along those lines, we pay. I also will cover my childrens friends when I know the parents simply cant afford something; Im doing that for *my* child.
But, if I were expected to pay $30 admission into the local water park every time my kids invited a friend, they wouldnt be allowed to invite friends very oftennot fun. That can get pricey. And some kids treat you like a bank. We have an entertainment complexbowling, laser tag, video games, etc. Some kids spend like nothing and keep expecting you to fork out more and then get very pouty when you say enough is enough, and it completely ruins the day for everyone. If they know they have to spend their own money (another adult training thing), they tend to be more prudent with what they spend and dont throw fits.