Physical training does not have to be boring. Here you have a collection of exercises, which benefits strength, balance and suppleness.

Use the hips to push each other out of balance.	Stand with the back to each other and the arms hooked together. Pull each other around. Watch out for violent moves.
Put your rear against each other and push.	Try to step on each others toes. You can include, that they shall try to touch each others shoulders. Remember shoes.
Place the hands on each others shoulders and push.	Take each others hands. Pull the other out of balance.
Sit down with the topside of your back against each other. Press against each other.	Stand on four with the shoulders against each other. Pres.
Lie down face to face. Arm wrestling	As in arm wrestling you can also leg wrestle
The one part lies down on the belly and "sucks to the ground". The other shall try to turn the first part around  to his back.	The one part lies on four. The other tries to push the person down
Standing on hands and toes the two tries to hit each others hands (no fist allowed)	Sitting on the rear with the feet against each other they push against each other and at the same time keeping their balance.