I was pleased to find that Iona Opie is still alive. Wikipedia gives this entry about the collection:
'Iona Opie is a world authority on children's rhymes, street & playground games and the Mother Goose tradition. Together with her husband she conducted primary fieldwork, as well as library research, interviewing thousands of children. The couple were also noted anthologists.
The Opie's collection is the richest library of children's books and ephemera and covers the 16th to 20th century. It was begun in 1944, amounting in the end to 20,000 pieces. It was donated to the Bodleian Library in 1988, after a two-year public appeal raised the £500,000 cost. The Opie's book collection is increasingly being transferred to microfiche. The Opies' large collection of historic toys and games is still owned by Iona Opie.'