The concept is that we are in an avatar relationship with our body. That means we are subject to influences from our human's in instincts and body abilities. I do not know if we seek a body that has special needs so that we can have that kind of experience. However, if the hypothesis is correct, then the short life of a baby is just a short experience in this venue. If we are immortal, then there is presumably time to try again.
As for the baby body, following Rupert Sheldrake's theories, it appears, the conscious aspect and its etheric personality counterpart appears to be part of a human collective to which its experience goes, not as a personality seeking understanding, but as a contribution to the collective memory of the species. That theory needs work, but it does not appear to be a matter of simple cessation of existence.
Thank you so much for the reply. That's honestly the best answer I've gotten and find myself comforted by it.
Do we know at what point in development the body gets a soul?
When the avatar entanglement occurs should be able to be established by applying the Implicit Cosmology, but we have no real data on that. My guess is that it cannot occur before the baby leaves the mother's auric field.