[boyce]

"The only reason it acts like a baby when born is to acclimatize itself with the ways of this Earth.... and to let it's body or shell grow."

That's a little simplistic but logical for a soul who has not previously incarnated, a 'first-timer'.

This world is not populated solely by first-timers, though, and those who have experienced other incarnations will already be at least slightly familiar with conditions here. Theirs will be a different situation but even a soul with previous experience won't be familiar with its new, immature body.

The soul / spirit has to wait while mobility, limb control and communication skills develop and mature over a number of years. We do, of course, see some children develop more quickly than others and that may be down to the pre-existing spiritual progression of the soul / spirit animating it.