GroupMe is a mobile group messaging app that you can download for free for the Android phones. There isn’t anything malicious about the design, but it does allow kids to send images and GIFs as well as group texts without using data. This means, you may think that you are stopping them by limiting their data, but with an app like this one, they can work around that.
Also, the GIFs and images that can be sent are not filtered so adult themes (i.e. porn) is easily transmitted this way.