但是我担心使孩子假装成父亲 用英语怎么说 是虚拟语气吧？

是的, if引导虚拟语句,从句用叙述句的方式 不需倒置

I am worrying about if the children pretend to be the father.

不是
but,i pretend to make children to be a father.

But to pretend that I am worried that the children into father

应该是But to pretend that I am worried that the children into father.