As far as Children's apps are concerned, the guidelines have been revised to more closely match the federal Children's Online Privacy Protection Act (COPPA) and also allow for Apple's wishes to let children 13 and younger have their own iTunes account. New restrictions prevent developers from seeking pictures, voice recordings and video from minors. That is in addition to current restrictions that prevent developers from obtaining the name, address and telephone number of minors.
Developers are allowed to ask for child's date of birth, but only to make sure that the site is not breaking the law. And the method used to obtain the age of the child must include "some useful functionality or entertainment value regardless of the user's age." In response to those situations where a minor used a parent's credit card without permission to make expensive in-app purchases, Apple is now requiring parental permission before in-app purchases can be made from a children's app.
source: Apple via TUAW, Engadget