Tin,
You meant Federal Stock Number.
Anyway, in doing some research I saw that two other wrenches popped up on fleaBay, another 41-W-603-25, and a 13/16" obstruction wrench with the FSN 41-W-1468-475. In both cases the brand is stamped as one word and one continuous string of letters - CHILDCRAFT - unlike yours, stamped as two terms - CHILD and CRAFT - on two lines, sharing the C. So I don't know if it's Child Craft or Childcraft. Either way, the only thing I am turning up are references to Childcraft Equipment Co., as far back as the 1930's, with furniture, and books.
It seems unlikely it's the same corporate entity, but if they made steel products, I might entertain the notion of them being forced into defense production, or converting to defense production on their own, which did happen.
To me the name looks like it's in the same category as Penncraft or Mechanicraft.
Links:
Childcraft obstruction wrench, 13/16
http://www.ebay.com/itm/Childcraft-...n-wrench-No-41-W-1468-475-E-155-/201916308291
Childcraft DBE brake wrench, 3/4 x 25/32
http://www.ebay.com/itm/Vintage-Chi...D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557
EDIT: And because the links are going to eventually disappear, photos...