according to IGI children are:

Otto Sydney WICHERT - International Genealogical Index
Gender: M Christening: 20 May 1866 Lezayre, Isle Of Man, England

Julius Butter WICKERT - International Genealogical Index
Gender: M Christening: 3 May 1868 Lezayre, Isle Of Man, England

Lina Augusta WICKHART - International Genealogical Index
Gender: F Christening: 10 Mar 1870 Lezayre, Isle Of Man, England

Charles Frederick WICKERT - International Genealogical Index
Gender: M Christening: 4 Feb 1874 Ramsey, Isle Of Man, England

Godfrey WICKERT - International Genealogical Index
Gender: M Christening: 15 Apr 1880 Ramsey, Isle Of Man, England

however 1881 census has:
Maughold 1 Bowring Road WICKERT Charles Otto Head M M 44 Master Of Ramsey Grammar School Professor Of Languages born Baden Germany
Maughold 1 Bowring Road WICKERT Mary Augusta Wife M F 38 Professor Of Languages Wife born Dublin Ireland
Maughold 1 Bowring Road WICKERT Otto Sidney Son - M 14 Scholar Ramsey IoM
Maughold 1 Bowring Road WICKERT Julius Buller Son - M 13 Scholar Ramsey IoM
Maughold 1 Bowring Road WICKERT Lina Augusta Daur - F 11 Scholar Ramsey IoM
Maughold 1 Bowring Road WICKERT Charles Fredk. Son - M 7 Scholar Ramsey IoM
Maughold 1 Bowring Road WICKERT Henry Adolphus Son - M 5 Scholar Ramsey IoM
Maughold 1 Bowring Road WICKERT Georgina Maud Daur - F 4 Scholar Ramsey IoM
Maughold 1 Bowring Road WICKERT Emily Florence Daur - F 3 Scholar Ramsey IoM

so the youngest child might have died ? - the missing two are probably explained by civil registration coming in 1877 and few parish registers extend past this date in IGI (not sure why the 1880 one is there )
General Registry will supply birth certs post 1877