That would genetically remove altruists from the population (assuming altuism is heritable and assuming children also have to press button).

The world would be a more selfish place in a generation after the experiment.

Presumably parents press the button for their babies.

As a family you would have to agree to all push the same colour otherwise you run the risk of only some of you dying. As a group decision I would think everyone would agree on red as the safe bet. Also making altruistic choices for children has two edges - and many parents would put their children's interests first not some strangers.