The question in 1911 asked how long a couple had been married and how many live children born and still alive to that marriage.
You will find that people often got a bit confused,some put down all children which belonged to a previous marriages,some entered miscarriages or stillbirths.Some wrote the names of those children who had died and you will find in some cases that the enumerator had to cross them out.
With an unusual surname you can search FreeBMD for births and deaths between censuses ,but not with a name like Harris,there will be hundreds.
Your best bet will be parish records,if they baptised their babies,and burial records(which HAD to be completed)
You can often work out where there is space for a child to be born,by the ages of the others.
First babies were often born within the first year, or even sooner sometimes,of marriage.
Carol