His birth is recorded without a mother's maiden name which usually indicates an unmarried mother:
Name: Mother's Maiden Surname:
HELLIAR, SAMUEL PURCHASE -
GRO Reference: 1848 S Quarter in YEOVIL Volume 10 Page 553
His entry in the 1851 census also confirms his mother Mary's unmarried status:
"England and Wales Census, 1851," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:SGGB-74J : 24 July 2016), Samuel Hellier in household of Mary Hellier, East Chinnock, Somerset, England; citing East Chinnock, Somerset, England, p. 23, from "1851 England, Scotland and Wales census," database and images, findmypast (http://www.findmypast.com : n.d.); citing PRO HO 107, The National Archives of the UK, Kew, Surrey
As to potential grandparents, I do see a Mary Hellier aged 19 living in Haselbury Plucknett in the 1841 census:
"England and Wales Census, 1841," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MQ1J-TKP : 30 October 2015), Mary Hellier in household of James Helliar, Haselbury Plucknett, Somerset, England; from "1841 England, Scotland and Wales census," database and images, findmypast (http://www.findmypast.com : n.d.); citing PRO HO 107, The National Archives, Kew, Surrey
Her parents are James and Hannah. In 1841 adult ages were meant to be rounded down to the nearest five so the websites automatically change an age to a range [age, age+4] and back out a range of years, but they do this even when the age wasn't rounded down! So ignore the age range - she was 19. The 1841 census was also later in the year than all subsequent ones (6 June) so if the 1841 and 1851 ages are accurate we can say that Mary was born between 31 March and 5 June 1822. That still leaves the question of why Edith isn't present but it was commonplace for girls of that age to be working as servants in another household.
