The little one I really think is a Huffman (Huffy). The fork crown, chain wheel and dropouts look a lot like this 1949 Huffman bike.
On the blue DX, it has a Schwinn crankset and chain guard. They put a 2 digit date on some of the cranks back then. That might be the answer to that puzzle. Here's an example of a 1937 crank:
I did some more research on the serial number on that Schwinn. I found this Schwinn on a page about their numbers but it didn't give the year of that bike. Small world. My lists say 1952 had 6 numbers, maybe they went to 5 at the end of the year. So 1952 is now my guess.
On the blue DX, it has a Schwinn crankset and chain guard. They put a 2 digit date on some of the cranks back then. That might be the answer to that puzzle. Here's an example of a 1937 crank:
I did some more research on the serial number on that Schwinn. I found this Schwinn on a page about their numbers but it didn't give the year of that bike. Small world. My lists say 1952 had 6 numbers, maybe they went to 5 at the end of the year. So 1952 is now my guess.