The Pincher Kiddies were the old-time navvies; the building trade equivalent of the the 'Shellback' - the sailors who had no homes other than the ships they sailed in.
This is a good description of them from, 'The Men Who Built Britain; The history of the Irish Navvy', by Ultan Cowley:

Pincher Kiddies
Bill Brennan (who found a home in Arlington House and a place in the British Medical Journal as the only individual on record with ten clubbed fingers, smashed on site) came under the influence of the old 'Pincher Kiddies' as a youth. He learned the techniques of tramping from them, in England, in the 1940s:
The Pinchers never advised any of us younger men, 'Learn a trade, don't settle for this'.... They'd never take another man's tools.... Each had his own, washed and spotless, tied up with a leather strap — their own 'graft', fork, foot-iron.... These were often pawned in Ryan's of Warren Street on a Saturday. The foot-iron was a great thing; you strapped this strip of steel under your boot between sole and heel to protect the leather from the digging. Out in a place like High Wycombe, flinty ground, boots without the foot-iron wouldn't last a week.
They had a kit bag, with a billycan, and a ball of twine and a six-inch nail for hanging up your billycan when you were sleepin' out. The best place to 'skipper up' [sleep out] was always under a palm tree — the water was all carried out to the ends of the leaves and wouldn't drip down on your clothes. The old Pinchers always told me, 'When you're in a town, always walk to the kerb, not near the doors, so if someone comes out at you, you can dodge'....
They knew where everyone was — if there was a job, they'd tell you, better than today. But they had the wanderlust — no matter how good the money, or the job, how well they were treated, for no reason they might say, 'I'm jackin'— I'm off. He might be diggin', you might be chasin', and he'd just look, up.... Ah, it's time I was movin' on', and he'd jus; walk away.... You mightn't meet him again for two or three years.
They were a great race of people — a mighty people. Regimental men — not educated, but they knew their work ... better than any machine today. Neat, and tidy, and yet they'd maybe be sleepin', under hedges. You'd know them by the neck-scarf and the moleskins, and the 'Yorks', and the hobnail boots.
Jim Gallagher also commented on the legendary footloose character of the Long-Distance Men, with whom he worked in the 1950s, saying that such a man might be beside him in the trench, when,
The head would come up, and look around, and he'd reach over for his jacket, and be ready for the off, like the mountain ewe [the nomadic hill-country sheep of the west of Ireland].
These men were unsuited to the new-style hostel accommodation, which was run along military lines, and often staffed by ex-servicemen. Only the Rowton Houses, such as Arlington, still retained to some degree the sort of semi-charitable system that had characterised the pre-war lodgings of the tramping fraternity.
A lot of men went into digs that shouldn't have been there at all — they'd wet the beds, an' all that, they couldn't help it. The 'Pincher Kiddies' — the 'Mile¬stone Inspectors', their kidneys were weak from years of sleepin' out under hedges.

Jim Carroll