foraging material
and perhaps bedding is what I have seen on several occasions, e.g.

http://www.ciwf.org.uk/publications/GAP/GAP_Chapter_7.pdf
Barren environments
In a natural environment, 3 week-old piglets start
to develop their foraging behaviours by beginning to
sample solid food items. The lack of suitable
foraging material in the farrowing accommodation
means that the piglets may start biting and chewing
at the sow causing discomfort, irritation and,
sometimes, serious injury. The lack of bedding
leads to increased restlessness, aggression and
injuries amongst the piglets.

http://www.efsa.europa.eu/EFSA/Scientific_Opinion/ahaw_op_ej...
foraging and nest-building material

On one occasion - although these were called 'legetøj' in Danish - I have seen 'toys' suggested for objects that were hung up or placed in the sties for the piglets to investigate and play with. (large pieces of smooth wood washed up by the sea, a hanging plastic bucket and wellingtons as far as I remember from the picture. Sorry, but can't find it on the net or give a reference.)