I've found an Isabella Ellen Whitecross:
Sep q, 1863, Poplar, v 1c p 573
and one for David Alexander Whitecross:
Septq, 1872, Poplar, v 1c p 603
This would tie in with the James that I found earlier:
Only birth record that I can find for James Whitcross, jnr is:
James William Whitecross, Dec q, 1870, Poplar, v 1c p 613
However, there is also a Margaret in 1882 in Poplar which was after James's marriage to Sarah

Sorry - I think i cross posted with you - not sure about the Margaret b. 1882!