Lonemoon confirmed it, the child was indeed the spirit seed of the plane that he'd just taken over. Hong Meng's plane had been destroyed once, it was possible that a spirit seed had been created then but due to the subsequent collapse of the plane, he was accidentally drained to Void Land.
Originally, when a plane is destroyed, the spirit seed will also disappear following the original source. However, at that time, in order to save Hong Meng and the others, Godfiend sealed up the original source purple gas. Hence the spirit seed in Void Land did not disappear. Later on, Shen Ying reopened the plane and Lonemoon built Heavenly Dao, becoming the new manager, that was when the spirit seed awoke and took on a form.