To recap: Children of Rosalie so far
Winifred May Cole (Warboys on 1911 census) birth reg 1905 Q3 Royston Vol 03A P 741 mmn - (implied Cole - illegitimate)
Percy Warboys (on 1921 census) b 1911 birth reg not found, nor any trace of him after 1921
Ethel Annie Warboys (on 1921 census) birth reg 1912 Q4 Chesterton mmn Mead
Walter H Worboys (on 1921 census) birth reg as Herbert Walter 1915 Chesterton mmn Mead, birth date 19 Dec 1915 (from baptism record)
Ronald A (on 1921 census) 1917 birth reg 1917 Q3 Chesterton 3B 592 mmn Lawrence
Reginald G Warboys birth reg 1921 Q3 Chesterton 3b 741 mmn Lawrence
Gwennie Rosella Emily Worboys birth reg 1923 Q3 Chesterton 3b 682 mmn Lawrence
The change from Mead to Lawrence seems to have happened between 1915 and 1917.
Rosalie was born Mead mmn Fuller, but her mother was widowed when Rosalie was abt 2yrs old and subsequently married Thomas Cole.
Percy is the odd one, only found in 1921, presumably born just after the 1911 census, and never seen again. Can't find him as Cole, Mead, Lawrence or Worboys, unless he was not registered as Percy,
Added.
Walter Worboys married Rosalie Lawrence Q4 1915, Herbert Walter / Walter Herbert was registered with mmn Mead in Q1 1915, but baptism says birthdate 19 Dec 1915, could that be error on record and he was born in Dec 1914?