这里面没有从句,it 是形式宾语,后面的不定式是 to teach children to love books 是真正的宾语,名词短语 his crusade 是宾补。
句意:He made it his crusade to teach children to love books. 他把教育孩子热爱读书作为自己的奋斗目标。
类似例句如:
She made it her business to get to know the customers. 她把了解顾客当成了自己的职责。
He made it his object in life to find the island. 他把找到那座岛屿当成自己的人生目标。
I'll make it my priority to settle your problem. 我会优先解决你的问題。