Struggling to Work It Out

How do you explain to a 4 year old about what happened 100 years ago?
Coventry War Memorial Park in the sunshine. Tree planted to the memory of Pte E H Buckingham 2/7th Bn. R. Warwick. Regt, 1925

Some research:
He name was Edgar Herbert and he was only 19 when he was killed in action.

BUCKINGHAM Herbert Uncertain of this man's identification. He was probably Edgar Herbert Buckingham, Private 37766, 2nd/7th Battalion Royal Warwickshire Regiment. He was born at Coventry, enlisted at Cheltenham, Gloucestershire and resided at Coventry. Killed in action 14th April 1918. No known grave. Commemorated on the Ploegsteert Memorial, Comines-Warneton, Hainaut, Belgium. Panel 2 & 3.

(The Royal Warwickshire Regiment, 2/7th Battalion. Formed in Coventry in October 1914 as a second line battalion - Territorial Force).