Take advantage of the power of the sun. Even a playhouse can have a great usage of solar power, for example for a LED powered lamp for lights in the house. Or to offer a power for a smartphone or iPod. So you need to install no electricity in a children playhouse, which could make the worst case for very nasty accidents. On the other hand you get this kind of power entirely for free.
The laying of the cable and attaching of the solar panels actually is quite simple.