Is there any scientific research that proves sleep-talk (reading affirmations to a child when the child sleeps) works? The promoters such as these https://gouldingprocess.com/ already say it does, but I want to be sure this is actually the case.
Google Scholar should be everyone's best friend for finding research results :)
Searching " "Sleep talk" hypnosis" (with "Sleep talk" in additional quotes to force google to find the exact phrase) yielded a lot of results about talking in one's sleep but about half way down the first page of results this gem came up:
Hypnosis for Children Using Direct and Indirect Approaches Kakoschke, Celia. Australian Journal of Clinical Hypnotherapy and Hypnosis; Brisbane Vol. 28, Iss. 1, (Autumn 2007): 39-44.
It appears to be directly referencing the "Sleep talk" as linked in the OP.
I don't have access to the full text but perhaps it can be requested through a library or local university or even just purchased if the interest is there. The introduction is available online at least and it confirms that it is on topic.