The speaker is giving thanks for a child-like way of thinking, one that never fully switches off. At noon and at midnight, it keeps busy making things out of "found carcasses," which could mean scraps, leftovers, or dead things picked up along the way. The word "carcasses" is a little grim, but the speaker seems happy with the results: the things are made "to my content," so the work satisfies.
The last two lines turn slightly. What the child-mind makes "quite overthrow[s]" how the speaker believes they ought to see. In other words, the playful, scavenging imagination upsets the adult's settled habits of perception. The speaker doesn't sound upset about this. The tone is grateful, a bit wry, and quietly surprised.
The mood is calm but lively, with a hint of darkness underneath. The title, "Erasure," suggests that something is being wiped out, perhaps the grown-up way of looking, to make room for something fresher.