Darren, it just proves what I said in answer to your original post on the Lancashire Archives look-up thread that if you posted on a different board the enquiry would attract interest and hopefully some relevant information.
A hawker was someone who sold items out of doors rather than in a shop. They were supposed to buy a hawker's licence from town council but some didn't. Some of those who didn't buy licences might occasionally be arrested and charged with selling without a licence. A lot of Irish or people who had no other employment did it. I read recently that it was the commonest occupation of Irish women in England on one census. (I didn't take a note of source.) Browsing a 19thC census in a working-class area of a large town or city with a significant Irish population, one notices groups of hawkers in cheap lodging houses. Your people may have gone door-to-door or stood in a busy street with their wares. They may have travelled to other towns and villages, depending on what they had to offer. Items they were selling could have been anything from food to brushes.
Plenty of reasons you haven't found them on a census:
They might be there but hidden because names recorded on census forms and then copied into census books may not be what you expect them to be. As John couldn't write (and Bridget probably couldn't either), names on forms would be written as the person doing the writing heard them and thought they might be spelled. A census enumerator then had to decipher those names and copy them into the census enumerator's book. A modern transcriber has to decipher old handwriting (or scrawl) in the census enumerator's books to create present-day indexes. Lots of opportunities for mistakes in transcription. Even worse with Irish names which may have been unfamiliar to census clerks and spoken with a brogue.
They might have been in and out of the workhouse a few times. Families were split up on admission. A person's details on census may have been incorrect or incomplete.
Being hawkers they might have been travelling around. Census enumerators had instructions to find out if people were sleeping in outhouses or tents etc.
They may have been in another part of the UK at census time. They might have gone back to Ireland or to Scotland. There was an extensive railway system by late 19thC with cheap 3rd class tickets. Also frequent, cheap sea-crossings through several Lancashire, Irish and Scottish ports.
What address was on John Junior's 1873 birth certificate? Have you checked this address on 1871 census to see who was there? Browse the street and area nearby. They would have been in cheap lodgings and may have moved frequently but might not have gone far.
