What size sim card for ipad 4th generation?
No context provided
What size sim card for ipad pro 4th generation?
Micro-SIM
No context provided
What size sim card for ipad mini 4th generation?
Nano-SIM
iPad Mini 4
https://en.wikipedia.org/wiki/iPad%20Mini%204
iPad (3rd generation)
https://en.wikipedia.org/wiki/iPad%20%283rd%20generation%29
The fourth generation iPad Pro[a] is a line of tablet computers designed, developed and marketed by Apple Inc. Two models, with a 12.9 inch or 11 inch screen, were both announced on March 18, 2020, and released on March 25.
IPad Pro (4th generation)
The iPad Mini 4 (stylized and marketed as iPad mini 4)[4] is the fourth-generation iPad Mini tablet computer designed, developed and marketed by Apple Inc. It was announced along with the iPad Pro on September 9, 2015, and released the same day. 
IPad Mini 4
The fourth generation iPad Pro is a line of tablet computers designed, developed and marketed by Apple Inc., and includes two models, one with a 12.9 inch and one with a 11 inch screen. The sim card size for the iPad pro 4th generation is Micro-SIM. The iPad Mini 4 is the fourth-generation iPad Mini tablet computer designed, developed and marketed by Apple Inc and was announced and released on September 9, 2015. The sim card size for the iPad mini 4th generation is Nano-SIM.