【中文这样说】

这个持刀疯子在幼儿园乱跑, 孩子们处于危险之中/冒着很大危险。

【英文对比翻译】

Chinese Style The children were very dangerous as the knife-wielding madman was running amok in the kindergarten.
American Style The children were in great danger as the knife-wielding madman was running amok in the kindergarten.

Dangerous危险的,用在这里表示孩子们可能给其他人或物造成危险,显然是错误的；in great danger 表示处于危险之中,冒很大危险.显然这里是说孩子们处于危险中,而不是孩子们对其他人造成危险。