First, the kid at the next table would have to be Stretch Armstrong to reach a cup on my table. And second, I keep my hot beverages, as well as knives and anything else that could harm a child, on the other side, away from them. Might just be me. Third, It's not the restaurant's fault if by some chance the long-limbed kid at the next table dumps over the coffee I carelessly left next to the child at mine. It's a toss-up between me as the responsible adult in charge of my table and my child, and the parent of the other child that should have been watching that kid better. I know, I know. Accidents happen. That's why they aren't called on-purposes. But a little due diligence goes a long way.
Do I think McDondald's should have turned down the temperature? Absolutely. And I'm glad they did. But I do not think that McD's is responsible for what people do with food or beverage after it's been claimed by the consumer. After cash and goods exchange hands, it's the property, and the responsibility, of the person that bought it.