^Distinctness (even in sense of the person being distinct from the environment) seems to be not that existent in toddlers, though. And afaik the first realisations of themselves as distinct happen after they have developed some lingual skills and are introduced to what the mirror is as well.
Moreover a toddler is mostly immobile in his cradle/similar small environment, and the external world may appear much like an extension of his/her own being. Iirc i recall (very vaguely of course) how i was looking (less than 1 year old obviously) at the living room behind the wooden protective bars of my toddler-space, and being of the impression that the room was also myself (or similar).
But change is picked up even by non-sentient beings. It is unlikely an ant is sentient (as in self-aware), but it is very obvious it will react if you try to hunt it down or pester it with some object.