According to an elderly cousin "They were in Swansea in south Wales in 1946. I do not remember their address, though it was near the railway line down to the shore and I remember coal wagons going by. One day we went to Mumbles, in the Gower Peninsula, where I collected shells on the sandy beach".
Would this information be enough to be able to pin point in what area they lived?
I think there are 2 possible areas, both quite large, that this could suggest:
1. Somewhere in the Swansea Valley, where railway lines came south from Morrison (on the west side of the river) and Llansamlet (on the east side), to the railway station/shore. This was the industrialised and far more populous side of Swansea and if the trains were carrying coal, this is probably the more likely.
2. But another possibility would be the Clyne Valley, out of town towards the west, where trains ran through the Clyne Valley from Gowerton to Blackpill. This was a less industrialised route, but there was a brickworks in the Clyne Valley itself so I presume that there would have been some trains carrying fuel.
Mumbles is not actually on Gower but is sometimes called the gateway to Gower! It was a popular day trip from all over Swansea (still is!) and a light tramway ran along the seafront from the centre of the town, passing through Blackpill and on to Mumbles - so I'm afraid that memory wouldn't help locate your family.
Here's a link to old maps which might help you narrow the search if you get some more info:
http://www.rootschat.com/links/01i4q/