The W2 should already take care of this. There might be a Saver's Credit, if their income is low enough.

As for Kansas, this is what Kansas explains for their W2 entries:

https://www.ksrevenue.gov/kpers.html

"The amount you contributed from your salary to Kansas Public Employees’ Retirement System (KPERS) is subject to Kansas Income Tax. Since the amount contributed is not subject to Federal Income Tax you will need to make a specific entry on your Kansas Income Tax Return. The entry will be on line A2 of Schedule S of the Kansas Income Tax Return. The amount entered will be the total amount you contributed to KPERS during the past calendar year. This amount can be found in Box #14 (identified as “KPER”) on your W-2."