6 year old children going missing is news. Getting it in there as soon as it became clear they were genuine missing might have meant a member of the public saw it and spotted them before it got dark
They were noticed missing at 7ish, and there was only an hour or so of daylight left. The police would have acted swiftly, but even so getting a general alert out before sunset was unlikely.
It's on several media outlets now, appearing from just after 9pm