I played VV1 and never knew about piling kids on a mushroom, so never even thought to try it. I read about it here while playing VV2 and have tried it a couple of times and even though it says they have a mushroom, only one is actually carrying the mushroom, at least in my game. I have never tried it on a collectible as I was afraid I'd just simply lose the collectible. Now you have me curious, I'll try it on the next common collectible.:)