I have 2 iPads. Should they both have the same id?
No, your Apple ID email/password combination will be the same everywhere - on your iOS devices, computers, and online. You can use it on as many devices as you would like and it will always work just fine - regardless of the device. 

Unrelated to that though, I would consider setting up a new Apple ID for your daughter and then configuring Family Sharing to link the two. Apple IDs are very much designed for one user per Apple ID. 

Aside from that, make sure you are entering the Apple ID username/password combination correctly and it will work.