Drug study on kids won't require consent

An interesting article from USA TODAY
As with the polyheme trial this takes advantage of the federal rule that allows researchers to test on human subjects without consent in emergencies. Unlike the polyheme trial this is aimed at children rather than adults.

The study assesses how two reasonably well tested drugs work in children whose seizures last over 30 minutes. While these drugs are in common use with adults they are not currently validated for usage with children.

While I can understand why the researchers want to carry out this trial, I am unclear why it is required to be done without consent? Could they not identify a population likely to seize, get prior consent from their families and then treat if/when they come in. This would of course be more expensive, but it would seem more ethical.