Well, to answer this question I must first analyse both the sources, source B is a picture depicting what seems to be a class of evacuees and their teacher walking down the road, probably to the train station to be evacuated. The picture shows many of the children waving and smiling, and what seems like a lot of them skipping, showing them being happy about being evacuated. Being a photograph, it is quite unlikely that it has been changed in any way, or staged to show the children being happy, as the scene seems quite natural.
However it is still possible that it was staged by the government at the time to encourage people not to resist evacuating their children, this would be done by showing the children happy and carefree, not afraid or worried about it. Also the picture was taken at the start of the war, when not many people had been evacuated, at this time the children and their families may not know exactly where they were going, and may have treated it like a holiday, so therefore they probably wouldn’t be to afraid about what was happening.
So, overall this source is quite a useful source, but that of course depends on what for, it is useful for showing children’s reactions to being evacuated at the start of the war, however this wouldn’t be useful for any time before or after this, limiting its usefulness. This also could, if it was a staged photograph by the government, be useful for showing what the government wanted people to think.
Source C however is quite different to the previous source, this is an interview with a school teacher during the evacuation, in 1988, in this source, it offers a different view of the children’s feelings about being evacuated, in this source, it tells us that the children were “afraid to talk”, showing that they weren’t care or worry free about the situation.
This source is primary evidence, as the person was there at the time, however this is taken in 1988, and the person could very well have forgotten some of the details of the evacuation, and therefore their memory of the event could be unreliable. However this might not be the case, and therefore it could be quite reliable. Overall, I think that source B is the most reliable, as it is a photograph taken at the time, and therefore the details of the situation would nearly definitely be correct, source C however is an account from memory and therefore the details could be wrong.
Source D is a photograph taken by the government during the war of evacuees being bathed, it shows three bath tubs close together with all the children washing and laughing, this scene would be likely to give the impression that the children, and the places they went to were hygienic, this would lessen the worries of the children’s families, and also may convince more people to become host families, because the children here seem healthy, clean and happy, not dirty smelly children with bad manners, as was many peoples views of them.
Also this may convince people to evacuate their children, as many families living in the cities were to poor to even bath their children, so this would be seen as an improvement in their lifestyle and living conditions.
Also, if this picture was taken after around January 1940, when many evacuees returned, many of their reasons being that they felt they were better of at home, and that life with the host families was unhappy, or the parents believed this to be so, then this photograph could be being used by the government to convince families to keep their children with host families, that life out there wasn’t as bad as it was made out to be. So overall I think that it really depends on when this photo was taken, which would determine why it was taken.