I've never seen/heard a safety message involving a child's voice.
I was, however, very interested in the reactions of passengers around me to the safety video on AirNZ either last or early this year; this was given largely by - I think- All Black rugby players. Some of these were recognisable to me, but a number of those around me spent the whole of the address debating who the people were and why they were doing the talking. I don't think any of them would have got the message.
Excellent no doubt for Kiwis, some Oz and South Africans and a few Brits, but Japanese Americans etc? Would have gone "straight past the outside edge" to use a cricketing metaphor!