The stated requirements are at least an iPad mini
2. Is that what you have, Cindyv10? If you have an IPad mini 2 or above, then I would suggest making sure that you've quit all other apps before running the game. If that doesn't help, you should contact the developers and let them know about the issue; you can use the form at the bottom of this page:
http://amanita-design.net/contact.htmlEdit: 1 GB of RAM or more is required to run the game on any iOS device; so you will need at least an iPad 3, an iPad mini 2, or an iPhone 5. You can use this list to determine how much RAM your device has:
https://en.m.wikipedia.org/wiki/List_of_iOS_devices