What explanations can you give for the father's wallet and the mother's scarf being in the nursery in "The Veldt"?

In "The Veldt" by Ray Bradbury, there is a nursery that creates a virtual reality--interestingly, since Bradbury's idea preceded the creation of this technological fact nowadays.  This reality of the nursery is controlled by the thoughts of those inside it;  it is "superreactionary, supersensitive color film and mental tape film behind glass screens."

On two separte entries into the nursery, George experiences the Africa reality; when he goes in alone, he finds an "old wallet" which he shows to Lydia.  On his second visit, he and David McClean discover the "bloody scarf" that George tells the psychologist belongs to Lydia.  Since the wallet has traces of saliva on it when George retrieves it, it seems that a lion has licked or chewed lightly on it, salivating at the scent of the man.  The bloody scarf suggests that the hateful thoughts of the children have gone further.  These items have probably been stolen from George and Lydia's bedroom and brought into the nursery by the children in order to perpetuate the reality of their hatred onto the "superreactionary, supersensitive" environment of the virtual reality of the veldt where thoughts exert control.  Having conditioned Africa sufficiently, the entry of George and Lydia after the children beckon them realizes the hatred of the children who have wished them dead.