Childe was an android made by the Fatui, they had been hopeful that they could recreate the Fatui harbinger after he’d been killed in battle against champion duellist Clorinde in Fontaine. Unfortunately the Fatui were unsuccessful because the android’s body was not durable enough to withstand many battles, so after erasing the robot’s programming system they dumped him in the forests of Sumeru where you found him being attacked by fungi while doing commissions for the adventurers guild