I think the only reason they put enter button is for players to read the new policy implemented by COPPA (Children Online Privacy Protection Act). That is also why you got a message asking you to enter your birth date
COPPA and Privacy Policy Update:
Backflip Studios is required under the Children Online Privacy Protection Act (COPPA), with limited exceptions, to obtain verifiable parental consent in order to collect, use, or disclose Personal Information (as defined below) from children. Many of our Apps are intended for general audiences and do not knowingly collect any personal information from children. When our Apps request age information from your child and your child indicates that he/she is under 13 years old, the App will block your child from providing personal information, including through social networking features. Please note, that if your child indicates that he/she is under the age of 13, your child WILL NOT be blocked from using our Apps. Your child will continue to be able to play our applications. However, since DragonVale park progress is stored on our servers for Android devices through Facebook, and a child under the age of 13 is not permitted to use Facebook, their progress will not be saved on our servers. Also note all users of DragonVale on the same device where a child has indicated their age to be under 13, will also no longer be able to use Facebook to save progress.