Minor Grand Daughter Apple ID continues to say Verification Failed

I created an Apple ID for my minor grand daughter to use my old iPad. I restored my old iPad to the original condition then set it up for her. I established and Apple ID for her according to the directions for setting up and ID for a minor child. It worked when I first set it up.

Now, when she goes to the App Store, it asks her to sign in with her Apple ID and when she does it says "Verification Failed - this Apple ID is not active." Then it continues to ask for her Apple ID Password, and each time it says "Verification Failed - the Apple ID is not active."

What now?