Hello Nicola,
Frederick's Army service records are available on Ancestry.
A quick scan reveals that he was a widower at the time he enlisted in November 1915 (aged 22)
Address: 15 Church Rd, Tettenhall Wood, W'hampton
Daughter: Dorothy May, b. 20/09/1914
Father: Thomas Picken
Mother: Elizabeth
Brothers: 1) Joseph, 2) Thomas Charles
Sisters: 1) Elizabeth Ann Butler, 2) Eleanor Shaw, 3) Annie Seal, 4) Caroline Buckley, 5) Susan Picken
MIC: British War Medal & Victory Medal
CWGC: Killed in action 01/08/1917 - interred at Ferme-Olivier Cemetery, Belgium / Plot 3. Row G. Grave 5.
Looks as though his personal possessions were sent to his daughter Dorothy, c/o Mrs. Annie E. Finney, of 27, Inkerman Street, Wolverhampton.
Regards,
Peter