Yeah, sucks to only have one rope.
Go to the hardware store and get 1 1/2" or 1 1/4" or 1" manilla. Oleg made his own splice and attachement system with old
grips he found and cut up and we would hang them on the high single rail on the Unevens.
Not 15-20', but perfect since the kids were only allowed to climb in V or straddle.
I like monotony. 3-5 attempts at climbing the rope. If they couldn't climb legless, I might help with a spot or they would sit in a straddle and pull their bum off the floor as many times as they could. On the one hand, I could spot to make them feel better about themself, OTOH it's a time suck so I might only spot one rope and stay there.
I generally don't time them but I know for climbs when they use legs, I give them 20-30 seconds or it just takes forever and cycles too slow with only 2 ropes, much less 1.
Fun ways to climb, two ropes at a time in L or hopping, upside down in straddle, upside down with feet or as slow as possible on one arm on the way down or up and taking one hand off to the side.
I no longer allow ANY climbs with feet unless I'm letting them have fun, especially with the younger ones. It's too much of a time suck. If we've already done our legless rope climbs for the day, I might come back and allow them to do more with legs to get more pull volume in at a lighter intensity.
Some other coaches send kids to the rope when they are misbehaving or messing around. I'm ok with leg assisted climbs then but I don't generally deal with such methods. I just send them to the wall or parent's benches instead.