From a humanistic point of view, the idea of a wishing well, or fountain for pennies, could be an opportunity to take stock of things as they are and think of something that might improve their life or the life of those around them.

By tossing a penny, or some token or sacrifice of their sincerity for the wish, it is not an empty wish, but they can pledge to do what is in their power to make that wish come true.

Perhaps by stating the wish out loud, or into the wind, they can take responsibility for fulfilling the wish so that it's not just an empty wish or promise with nothing backing it up. A person can actually attempt to make it come true.

Unlike a prayer to an outside deity, begging for some supernatural force to step in and rescue them or give them riches, the wishing well is an opportunity to put your money where your mouth is, or some elbow grease into your wish.

Just my thoughts, if I were to encourage a child to make a wish and toss a penny in... They are buying the opportunity to try to make it come true. So, realistic goals only, haha!

One of them is free.

Somebody collects the coins in the well and uses them, maybe for something good.

The chances of either one coming true are about the same but people that pray actuall believe the will come true! They obviousely are living in a fantasy world!