Solving the world's problems can be a difficult enterprise, but 150 children aged 8-12 had a go at it recently, in five cities around the globe.

In the first Global Children's Designathon, the students put in a hard day's work of designing solutions to problems that cities typically face, like poverty, waste, pollution, and congestion and then designing prototypes of machines or systems to solve those problems. The results, organizers said, were imaginative and forward-thinking.

Efforts took place in Amsterdam, Berlin, Dublin, Nairobi, and Rio de Janeiro. Organizers were from Unexpect, a Dutch design agency.

Working in teams of two and three, the students came up with such ideas as these:

• a smart car that signals traffic lights of the car's imminent arrival at an intersection
• a trash can that recycles plastic objects by shaping them into things
• a remote-controlled helicopter that performed twin Earth-friendly activities of scooping plastic up from landfills and oceans and then using a solar-powered flamethrower to melt the plastic so it could be shaped into beds for homeless people
• a street that divided itself so that garbage could slip underneath, into an underground landfill
• a trash-collecting robot that "eats" the trash and then transforms it into fuel
• a portable greenhouse system that can grow enough food to make a house self-sufficient
• a city smog sensor
• a telepathic communication system, to combat loneliness.

Then, it was on to building the prototypes. Some were easier to build than others.

The final step was to share ideas and prototypes with students in the other cities, via videoconferencing.

Organizers are already planning the 2015 event and want it to be much bigger.