Baptism dates

[kmdryd]

Hello.
Can someone please help me find the bap. date of my gx3 grandfather.
William Henry CLEMSON.  b.c.1807 (probably St. Marys Newington)
Also his siblings:

Ann      b.c. 1809  Tunbridge Wells. m. Thomas Pearson
George b.c. 1811 St. Marys Newington. m. Georgina Ching 1849 Lambeth

There is also  Matilda and Thomas, but have no approx. date for their births.  At a guess, maybe 1800 or 1805.

William Henry will not be on any English census as he came to Australia in 1824.

Parents of these children were George and Jane (nee Gale).
 
Any help at all, would be greatfully appreciated.
Kathleen