The National Deaf Childrens Society have published an FAQ on radio aids in the early years. This provides a summary of research published last year, and also responds to the various issues that have been raised since. This will be a live document and may be updated over time.
It can be dowloaded from the NDCS website at: https://www.ndcs.org.uk/document.rm?id=14049.
This FAQ is in addition to a briefing that NDCS recently published on radio aids safety with under 3s: http://www.ndcs.org.uk/document.rm?id=13887