Source: United States Federal Trade Commission

This diagram demonstrates how companies unknown to you can build a comprehensive profile about you (or your children) from smartphone apps - even if an individual app transmits limited personal data.

According to its Dec. 2012 report Mobile Apps for Kids: Disclosures Still Not Making the Grade, more than half of the 400 apps surveyed collected identifiying information. Most saved and transmitted the device's unique ID.

The large number of apps grabbing that information sent it to one of only 30 ad networks, analytics companies, or other third-parties. This small number of receiving companies can combine the data based on the device ID.

"Indeed, using the device ID and other information obtained from multiple apps, these third parties could potentially develop detailed profiles of the children using the apps, without a parent's knowledge or consent," the report stated.