I scratch your back, you scratch mine

It's a well-known fact that getting on the good side of other kids' parents substantially increases your chances of getting the help you want to enhance the fun of playground-playing. Take Richard, Maja's dad, for example. Yesterday, I got to ride on his shoulders to and from the Odynca playground. And I got to swing high and for a long time on the crazy low-placed swings. The likelihood that mom or dad would have gone down on their knees for that long is very limited.
Yet, however manipulative this may sound, there is a brilliant psychology in it that means you don't even have to feel guilty about taking advantage. You see, this is all part of a social game, rather than a function of altruism: Other kids' parents get on the good side of your parents by getting on well with you. And vice versa. Your parents get on the good side of other kids' parents by sucking up to their offspring. Now, for as long as this game goes on, all kids gets to swing high and everybody's happy.
(And once the parents know each other well enough not to have impress on each other's kids at the expense of knees and shoulders, you may have grown tired of the swings anyway.)