I don't find it but quite a few articles on the 'spirit' dolls seem to be going for the strange thai people angle.
'Luk Thep' seems to contemporise practice of Kuman Thong. (See https://en.wikipedia.org/wiki/Kuman_Thong)
While Kuman Thong was originally classified under a form of black magic, it has become a widespread practice and acceptable (the popular practice of keeping a kuman thong does not include the 'roasting' of human foetus).
My understanding of the popular Kuman thong practice - that it has become very different from the Chinese black magic practice of 'keeping a baby ghost' or Malay black magic practice of keeping a Toyol. How did keeping a child spirit become so widely practice in Thailand?