I'm assuming that it keeps crashing each time you give the flute. If so, the first step I would suggest is to make sure that all other apps are closed. If that doesn't stop the crashing, the second step I'd recommend is that you delete the game, then redownload it and reinstall it in order to see if that might solve the issue. I realize it's a pain to do that second step and have to replay the game up until that point, but it may solve the issue.
(I've played through the entire game on an iPad 4 without any crashes.)
If the crashing issue still happens after a reinstall, I would recommend contacting the developers to let them know about the issue. You can use the form at the bottom of this page:
http://amanita-design.net/contact.html