what does "they each had a pick-a-back "here mean?
No, it was true. Every morning when he came back
from chambers it was to find the babies with Isabel
in the back drawing- room. They were having rides
on the leopard skin thrown over the sofa back, or
they were playing shops with Isabel’s desk for a
counter, or Pad was sitting on the hearthrug rowing
away for dear life with a little brass fire- shovel, while
Johnny shot at pirates with the tongs. Every evening
they each had a pick- a- back up the narrow stairs to
their fat old Nanny.