Do you happen to know who the relatives are that were in Ruthin? I know Rhos St primary school and Ruthin Grammar School were both effectively on the same road.
The ancestor I'm researching (John Thomas Jones) and his wife ran the Anchor Inn which was at 1 Rhos St, and they had come from Birmingham to run the pub. So I do wonder whether they were involved with the evacuees at all, they didn't have children of their own.