You probably already know this, but the Social Security Death Index (SSDI) lists Caroline's son Wallace Olwood as born 30 Jan 1924, died 20 Dec 1992, last residence known to the Social Security department was Weymouth, Norfolk Co., Massachusetts. Wallace's social security number was issued in Massachusetts.
The SSDI shows another Olwood, named Edwin N. Olwood (who is probably the World War II veteran Edwin Neal Olwood that you can find in a search at Ancestry.com), born 24 Oct. 1925, died 7 Sept. 1982, last known residence in Virginia, social security number issued in Massachusetts. Since Wallace and Edwin both had their s.s. numbers issued in Massachusetts, and since Edwin was about a year and nine months younger than Wallace, it's possible that Edwin was Wallace's younger brother.
Of course that doesn't help us locate Wallace's mother Caroline Riggs Olwood, but it helps narrow down when your grandmother was married and when she had Wallace. If Wallace was born in Canada, then your grandmother must have married Wallace's father, say, around 1922-23. Also, I note that the 1929 Newton Massachusetts Directory at Ancestry.com lists your grandmother Caroline Olwood, so that also helps us track not only where she was living but when.
Do you know where in Canada your grandmother was born and where she lived while in Canada with her husband and her son Wallace?