Past and present tense

Marian has been able to understand the difference between past and present tense at least for the action to look and see. When I am reading a book with her she will use the past tense to tell me that she has seen it before. For instance we came back from the park having seen some ducks. When she spotted the duck in a book, she said seen. When she wants to read a particular book, she will say the present form.