Naruto is not the Destined Child (so far). Jiraiya believed he was the one (in the end). You know what I mean? If Jiraiya knew from the beginning Naruto was the destined child, why fight Pein till the end? He could try to escape and tell Naruto all he has learnt about Pein and his Jutsus don't you think?
He said so himself that he could escape if he wanted to, but he gave up his life to learn the truth.