Sharon from Sweet Pea & Pumkins shares a tutorial at the Oliver + S blog showing how to adapt their School Photo Dress to give it a hidden kangaroo pocket. The panels on the front of the dress allow you to add in this pocket without making significant alterations. Her tutorial is divided into 2 parts. Go to part 1. Go to part 2.
[photo from Sweet Pea & Pumkins on Oliver + S blog]