Well, Allen already told the president to send some people here. Because of this, the president quickly reacted and sent some of his people here.
If you are thinking why Brian quickly left, then it was because Brian still feared the guardians. He is now attacking the orphanage and normally he will get punished by the guardians. Because of this, he quickly left that area. Because the leader of that city has the power to contact the guardians.
Allen finally came out from his hiding place. He wasted no time and went toward the orphanage. Before anything he needed to check the condition of the Childers, Samantha and other people. Because of this, he quickly went toward the orphanage.
'Sigh,' he sighs in relief when he notices that nothing happened to them. Right they were sleeping comfortably. Allen, without making any sound, left that place.