Is there a way to keep the number keyboard up when entering numbers

Search the iOS App Store for "numeric keyboard." One, NuKey Numeric Keyboard, appears to give what you want and still runs on iOS 10.

If you think this is something Apple should make standard in iOS, you can use this feedback link to let them know:

Feedback - iPad - Apple

With the built in virtual keyboard, if you continue to type numbers or any of the characters on that keyboard the numbers stay in place. As soon as you hit the space bar or the return key, the keyboard goes back to letters.