Backstory: Most of my friends have kids now and they always chat about how they're driving them to one sports event or another. They talk about the time it takes and coordination with their spouse to pickup and drop off their kids from practice and events.
The Idea: Reliable and vetted child taxi service.
Deep Dive: You would have to develop an extensive screening and testing system for hiring and placing drivers. You would also equip the cars with cameras to monitor the drivers and kids. Once you solidify the vetting/logistics, you would build an app similar to Uber or Lyft but for kids.
Validation: Similar to how we as a society were nervous to jump in a strangers car for a ride (lyft or uber).... with the proper precautions and security we would be comfortable with placing our kids in a safe/secure vehicle for travel.
Monetization: You would take a percentage from each trip similar to uber/lyft.