Lynn
I was looking through some of the photographs on the imuseum website and came across one labelled "Mrs Kennaugh". It shows a woman in her 40s with 6 children around her, ranging in age from approx 6 to upper teens. From the youngest upwards they appear to be M, F, M, M, F, F.
The other imuseum photos of this particular type date from approx 1874/5. The children in this Kennaugh family group match the ages and girl/boy sequence of the six youngest members of your John Kennaugh/Margaret Jane Bridson family. I may have got the wrong Kennaugh family, but a quick look at the other Kennaughs who were producing children at this time doesn't reveal another family with this combination of girl/boy/ages. It's worth a look, anyway.
Jean