Mine have only chewed bars when they've wanted to get through them but it's not been persistent... then again mine might be older than yours as one is 2 and three are 3. Is there something interesting they can see that they might want to 'explore'? Can they see the hay bag? Do they fancy a bit of floor time!
I do a cage tidy and hay refresh in the evenings, but in the morning after a few veggies I give a handful of fresh hay to keep them busy while hubs goes on the 'grass run'. They still have plenty of hay from the night before but they're always delighted to get a bit of fresh on top!
Mine won't climb but young Flora could possibly jump a C&C if she was determined to do so because I've seen her jump effortlessly on top of the bars in this picture and perch there. This barrier is 27cm high which is 10&1/2 inches - she perched on the top wire like a bird. If there was a big drop on the other side I might think about whether I need an extra row of grids on top? Mine are on the floor - those on the right have the run of the kitchen, but if Flora fancies her chances on Zara's side of the fence... well, I suspect she'd rapidly jump back out again.
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