I've heard of issues in Mexico and Italy since those are both third-party restaurants.
One time, and I'm sorry but I can't remember where, we were told that the drink was not included when an adult ordered from the kids menu.
The larger portion thing was usually related to the dining plan. If you were redeeming an adult credit for a kids menu entrée, they'd bring a larger portion. I've never heard of anyone actually getting charged extra for a larger kids menu item when paying out of pocket. I'd probably need to see a receipt as proof of that claim.