I would be hesitant to give a toddler a Kooka Bay pad, but I wouldn't have problems with my son using one of the POE pads which use a heavier 50D/75D fabric, like the Classic AC or Adventurer AC. They're not the lightest, at 15 and 16 oz respectively, but I think they'd be pretty bomber. Both are rectangular.
I have an Ether Compact 6 that has gotten a beating from my 2 year old- jumping on it, falling on it, folding it and jumping on it, etc. I didn't mind because that model was never terribly expensive, I got a good deal on it, and have replaced it with a Kooka Bay pad for my own use. They used to make a rectangular Ether Compact 9, always a change you could find one of those in regular or 2/3 length.
Bender will make you a pad with 70D fabric instead of the standard 30D, but from what I understand the rest of the construction is the same. My Kooka Bay pad strikes me as something which needs to be treated somewhat gently, like most UL gear- while the valve itself is a Thermarest valve, the way it's attached feels less sturdy than the POE or most Thermarest pads. I don't mean to scare you or anyone else off- I just don't think it'd deal with the rigors of a toddler quite as well.
Z-Rest + Thomas Stickers = Moms FTW!