While the war was raging in Europe, the children were evacuated to a remote island.

raging 是动词 rage 的现在分词形式。rage 本意是"狂怒、暴怒"，引申为"（战争、风暴等）猛烈进行、肆虐"的意思。在这里表示战争正在欧洲激烈地进行着。