As a hypnotist who participated in past memory/life regression sessions I can offer only my opinion.

I think it is all wishful thinking.

That being said there are curious stories about children who claim to have a detailed experience that some claim is evidence of a deceased person in history. There are many explainations to account for these claims than just reincarnation or soul transferrence.

We may know children who seem to be old souls since they seem to have a level of sophistication that belies their years. We may be underestimating childhood consciousness or merely making a compariosn to other children who express less inate intelligence.

My wishful thinking opinion will naturally skew my perception of regressive hypnosis sessions that come claim as proof of a anachronistic consciousness. It is not proof but an opinion.

Giving extra attention to a child who behaves in a certain way is reinforcing of that behavior. It is also likely that an adult or parent have more to do with the unusual "phenomenon" than they will ever admit. Consider "baloon boy".