Answer:
The "infant" in the poem means the time when the earth was young.
Step-by-step explanation:
"Thanatopsis" by William Cullen Bryant was written as a means to acknowledge that we are all destined to die. Death is the universal equalizer that has no bias and is ultimately the only thing that will bring everyone on the same level. We all come from the earth and will return to earth again, no matter how reluctant we are to die or how rich or beautiful or mighty one may be. Death will ultimately take take claim of our lives and deal with it the same way it deals with the other humans too. The "infant" in the poem is suggestive of the fact that we will all be together in the ground with those who had died when the earth was young, meaning those Biblical figures or people from the far past- indicative of the fact that we will all be the same in the end.