Do you need to bring an ID? The kid doesn't have one.

No need, buying a mobile phone and opening the SMS QR code on it actually allows you to enter.
It’s not necessary to, you can also buy tickets and scan the QR code on your phone through Ctrip.
No need, scan the QR code displayed on your phone to enter.
It’s possible that you don’t need to; you can also buy tickets on Ctrip and scan the QR code with your mobile phone.