英语有个不懂得Although he was a child, he knew what was the right thing to do. 在这个让步状语从句

Although he was a child,he knew what was the right thing to do.
虽然他还小,但他知道做什么事是正确的.
在这个让步状语从句中,to do是起到形容词的作用,作为thing的定语.不定式做形容词？是。