Drawp is a nice iPad app that I recently learned about from Jo Villis. Drawp allows children to create drawings, take pictures, and create audio recordings to send to parents, grandparents, and other family members in a safe environment. To use the app parents have to register themselves and their children. Parents approve the list of people that their children can send messages to. After creating their digital greeting cards students share their work by tapping the share button and tapping the pictures of the people that they want to send their messages to.
Drawp could be a good app to have elementary school students use to send a weekly update to their parents about what they have done in your classroom.
Drawp is a freemium app. The basic uses of the app are free. You can purchase extra themes through in-app purchases that range in price from $0.99 to $4.99.
Maily is a similar app that you might want to try as well.