Yeos asked: “how does the manomaya kaya/karmic body sees the world through the eyes of a baby?”
Yes. One can think of as the gandhabba “trapped inside the physical body.”
All external sensory inputs come through the “doors” in the physical body. Vision comes through the eyes, sounds come through the ears, etc.
– Then those signals are processed by the brain and transmitted to the gandhabba inside.
– That is a simple explanation. For details one needs to read the following posts:
“Our Mental Body – Gandhabba“; see #8 specifically.
“Clarification of “Mental Body” and “Physical Body” – Different Types of “Kāya”
“Second question: it is said that “there is a nervous system in the gandhabba that overlays the physical nervous system.” Is there in the Tipitaka any other info describing what constitutes such nervous system?”
The Tipitaka may not have direct references to everything. We can figure out some things on our own. But the key references to gandhabba in the Tipitaka are at:
“Gandhabba State – Evidence from Tipiṭaka”