How do you play with rats ?

I made them an area for walking near the cage, before that I just threw them on the plaid on the sofa. Near the cage they like to run more. I made them a corner out of ordinary boxes, but they are not interested in it at all. Although what is the difference in a beautiful house to sit or in a box. Maybe I did something wrong?
What else would you add to their playground? How to organize? And how do you play with them? I only have balls and string. The gray rat sometimes grabs different objects, the same balls and drags them a little, sometimes runs after the ropes. But not for long. White rat isn't interested in these things. She's more interested in running up to me, grabbing my shirt. Or climb everywhere.

Any advice would be appreciated