Jock Tamson’s Bairns

Mankind, common humanity. Chiefly in we are all Jock Tamson’s bairns (and variants): used to express the belief that all people are equal, or to convey a feeling of fellowship, community, or shared interest.
“Jock Tamson’s bairns, n.” OED Online, Oxford University Press, March 2018, Accessed 25 May 2018.